Q:

Did NASA use CGI for the Apollo mission trainers?

The Ohio State "Press Book", Computer Graphics and Computer Animation: A Retrospective Overview talks about the training simulators used on the Apollo projects:

The visual images for the Apollo trainers, and the later Shuttle and Skylab trainers, moved to an entirely digital control. Window scenes were entirely computer generated. Coupled with sophisticated image processing techniques, the simulations could not only represent the environment of Earth and near space, but also the surfaces and environments of the Moon and Mars and other celestial bodies.

Is this paragraph truthful? Are there examples of the quality of this CGI?

A:

No
The page that you link to only weakly references this NASA page, which in turn is a digital version of a part of a book:  Encyclopedia of Computer Science and Technology, Volume 18, Supplement 3
The only showing of anything that can be considered a rendering of an alien world such as the Moon or Mars is at the bottom of the page. 

The image caption is: "Image processing makes possible scenes from alien worlds such as this panorama of the Martian surface."
Several issues here: 

The particular image in question is from the Viking 2 Lander, on Mars. It even says so in the text below. Camera 2 to be precise. Viking 2 landed in September 1976, long after first Moon landing. 
Image processing is not the same as fully 3D Computer Generated Imagery. The image processing technique they have employed there is image stitching, to make a panorama or — as it was called back then — a mosaic. And that too is visible in the image text. In the middle you can read: "COLOR MOSAIC OF RADCAM OUTPUT". 
You can even read the image IDs for the pictures they used for the stitching. The following links lead to those particular images in PDS v3 format (Planetary Data System). They contain meta data when the images were taken.

22A003 Taken September 4, 1976, from 03:48:44 UTC to 03:55:25 UTC (that is over 6 minutes). And here is 22A003 in JPG format. That is the middle one in the mosaic.
22A016 Taken Spetember 6. 
22A018 Also September 6, starting 10 minutes after 22A016.

There is nothing that connects that image with the Apollo simulators, other than that it appears on a web page that describes NASA's engineering simulators... all of them, from Mercury to the Space Shuttle. 
And here is the big kicker: that image is meant to illustrate the next section in the book: Image Processing, not the engineering simulators. It has simply ended up in the wrong chapter in the web version, as evidenced by the book itself.

So that image is not evidence for that CGI for the Apollo simulators was advanced enough to provide photo-realistic simulations of the Moon. 
The only mention to image rendering that is made is this passage: 

Actually, the Apollo Mission Simulators were the last of their type in that the analog environment of the spacecraft that dictated hybrid and functional simulations changed to a digital environment that lent itself to full digital simulations for the Shuttle program. Evolution to full digital simulation, including digital imaging of window scenes, meant even more dependence on digital computers.

That is to say it was not until the Shuttle Program that there was CGI — of any sort — of window scenes. Any even so it does not say that such CGI kicked off at such high quality graphics that they were enough to fool a casual observer into thinking it was reality.
Since that chapter is the only thing that the original claim in "Computer Graphics and Computer Animation: A Retrospective Overview" references, there is no support for the claim that Apollo era simulators had high quality CGI. 
And in any case it is self-evident that computer rendering at the time of the Moon landings was not even close to producing the kind of moving images that were shown to the public. It was not until 1988 — 20 years after the first human-crewed Apollo flights — with Pixar's short "Tin Toy" that we got a computer rendered animation of a human. 

A:

Is this paragraph truthful?

Yes, but not in the way you think. No CGI was done, merely digital control of still imagery.
The claim:

The visual images for the Apollo trainers [...] moved to an entirely digital control.

Hijacking MichaelK's link to the NASA site, we find this (emphasis mine):

Requirements for realism increase the complexity of the simulation. For example, when an astronaut fires thrusters, the simulator must activate readouts and lights showing the thrusters firing, fuel reducing, velocity changes, and also show movement in the scene outside the cabin window. In a moving base simulator, such as a simulator in which a spacecraft cabin is suspended on hydraulically moved pylons to enable it to tilt, physical motion must take place. Causing all these things to happen and coordinating them to happen simultaneously is the difficult task of the simulator designer.
[...]
Analog computers commonly supported simulation in the 1950s and early 1960s. Having the advantage of great speed, the electronic analog computer fit well into the then analog world of the aircraft cockpit and its displays. By 1961, though, it became obvious that the simulation of a complete orbital mission would be impossible using only analog techniques. The types and number of inputs and calculations stretched the capabilities of such machines so that when NASA defined requirements for Gemini simulators, digital computers dominated the design. 

But note that this does not mean that what you saw when looking out of the window of his trainer was digitally created, it was merely digitally controlled. This is not about CGI, this is about making the pre-processed imagery you see when looking out of the window turn according to control inputs.
This is made explicit a bit further down the page (emphasis mine):

Scene depiction in the Gemini era still depended on the use of television cameras and fake "spacescapes", as in aircraft simulators. Models or large photographs of the earth from space provided scenes that were picked up by a television camera on a moving mount. Signals from the computers moved the camera, thus changing the scene visible from the spacecraft "windows," actually CRTs.

The idea that these machines would create photo-realistic imagery on-the-fly is ludicrous if you look at what they were working with at the time:

The sets of computers could communicate among themselves by using 8K words of common memory, where information needed throughout the simulation could be stored. [...] Over 350,000 words of programs and data eventually ran in the two simulators.

They later ran into problems when the DDP-224's had trouble simulating the Apollo Guidance Computer... that's not the kind of hardware that could run CGI of any description.

Are there examples of the quality of this CGI?

No CGI was done. What the computers did was moving a camera pointing at pre-processed still imagery.

Digital image generation did not happen until the Space Shuttle. Same source, emphasis mine:

Actually, the Apollo Mission Simulators were the last of their type in that the analog environment of the spacecraft that dictated hybrid and functional simulations changed to a digital environment that lent itself to full digital simulations for the Shuttle program. Evolution to full digital simulation, including digital imaging of window scenes, meant even more dependence on digital computers. Making the Shuttle a more autonomous and thus more complex spacecraft contributed to a massive increase in the size of the computer systems needed to support simulations.

A:

There is detailed information in the March 1973 NASA report APOLLO EXPERIENCE REPORT - SIMULATION OF MANNED SPACE FLIGHT FOR CREW TRAINING: 

Both the TV/model and electronic image
  techniques have produced satisfactory
  displays for station keeping and docking. In
  the EIG technique, complex shapes cannot
  be drawn; therefore, realism is significantly
  less. Conversely, the EIG is a much
  simpler system to maintain and operate.  

...  

Two general techniques have been used for target-vehicle simulation: a direct
  analog system of closed-circuit TV and models, and an electronically generated (drawn)
  image. In both systems, the input to the display system was through a CRT in the infinity
  optics systems. The electronic image generator (EIG) was used successfully in
  one of the Gemini mission simulators, in the Gemini part-task trainer, and in the
  LMPS. In the EIG system, the target vehicle was drawn on the face of the CRT. The
  outline or envelope of the target was drawn at a 60-hertz rate; however, the surface
  was filled in at a 15.75-kilohertz rate. The image generation contained nine degrees
  of freedom and produced such phenomena as line-of-sight blanking, illumination
  shadowing, and perspective distortion. Simple target shapes (cylinders, cones, and
  others) as well as combinations of these shapes were readily simulated with simple
  surface markings and details. 

...   

Landing scene simulation was required only in the LMS for training in the lunar
  approach and landing phases. The altitude range desired was from a high-gate or
  breakout altitude down to and including touchdown. The scene was required to provide
  the crewmember with attitude and altitude information plus pertinent surface-feature
  details. In all other programs (for instance, during earth entry and landing), there was
  a minimum of crew activity relative to the window displays; therefore, little or no external
  scene simulation was supplied. In the LMS, the requirement was defined as a
  continuous scene from an altitude of approximately 15 000 feet to touchdown. The original
  requirement at the time of simulator procurement was for a generalized lunar surface
  containing representative features of the moon. This requirement was expanded
  subsequently to include modeling of the actual landing sites. Three-dimensional surface
  detail was required when surface irregularities became visible to the crewman.
  For the lunar landing simulation, the attitude at which surface features became important
  was defined as 2000 feet. An additional requirement was the casting of shadows
  such as would be caused by local surface irregularities when illuminated with collimated
  sunlight.  

...   

As initially delivered, the LMS was designed to meet the specified 15 000-footaltitude
  range capability with a combination of the closed-circuit TV/film technique described
  previously for near-body scenes, and a relatively conventional closed-circuit
  TV/3-D model system. This model system, known as the landing and ascent (L&A)
  system, was used below 1200 feet. The model was 1:1000 scale with three typical terrain
  types arranged in 120 [degree] pie sections; one each for hummocks and small fissures,
  boulders and large fissures, and craters. The distribution of these features was such
  that approximately 35 percent of the surface could be used for landing. Shadows were
  simulated by painting the model. The solar elevation angle was assumed to be 45 [degrees] .
  Overall, this system was determined to be inadequate for training. The major shortcoming
  was the lack of continuity from breakout to touchdown caused by the film system
  problems mentioned in the discussion of near-body scenes. An additional shortcoming
  was the lack of realism in the landing area model. An upgraded system, which used a
  3-D model from breakout altitude to touchdown, was developed for training of the first
  lunar landing mission crews. Maximum altitude of the model simulation was increased
  to approximately 12 000 feet, and the model scale was established at 1:2000. Two significant
  features were added - an accurate model of the targeted landing area and a
  collimated light source to illuminate the surface and produce lunar-terrain shadows.  

...  

Two LMS's (fig. 4), one located at MSC and the other at KSC, provided the training
  for the LM portion of the Apollo missions. The two simulators were designed, built,
  and maintained to be identical. They consisted of an instructor and operator control
  console, an infinity optics display system for complete out-the-window scene simulation,
  a high-fidelity representation of the LM crew station, and a three-machine digital computer
  complex. The digital computers were the same as those used in the CMS. Also
  as in the CMS, one computer was assigned exclusively to simulation of the onboard guidance computer. A significant portion of the LMS, which provided training for final
  touchdown, was the L&A visual display system. This system included a lunar terrain
  model (scale 1:2000) of the specific landing site for each mission.

 
(image source: NASA)
So in conclusion, primarily the simulators relied upon three dimensional models of the lunar surface for imagery, with computers controling what views of models would be seen at a given moment.  While NASA did have the ability to generate images electronically, the resolution was very low.  

