Will two spacers between the cassette and the hub effect the chain line? So I have a set of custom wheels (White Industries T11 hubs) and when the cassette is correctly fastened to the hub with the single spacer provided the cassette cogs can be moved in the direction around the cassette (not laterally) ever so slightly. This causes an audible klank when the cogs are engaged and is generally not good. The solution from the wheel builder was to add an additional spacer between the hub and the cassette. Both spacers used were shipped with the White industry hub.

Using two spacers completely fixes the cassette slip issue but I'm wondering if it is effecting the chain line in some way? I have used the set of wheels on two different frames both with Ultegra group sets. 

It could be me but there seems to be slightly more chain rub with the White Industry wheels than other wheels I have used like Mavics. Keep in mind that I am resetting both the front and rear derailers to accommodate the shift. Is it possible the spacers are just too wide? And are there different sizes for these spacers. Thanks in advance, any experience or advice would be appriciated.

I'm using a 10 speed setup, first bike is a Ridley X-fire (54) second bike is a Sworks Tarmac(58).
You're thinking about this from the wrong side of the cassette. All cassettes end at roughly the same point or the lockring wouldn't engage correctly. The spacers are to make sure there is significant compression, but because the cassette is still in the same spot relative to the drive side of the wheel the chainline shouldn't change. 

That said you might want to pick up some different size spacers and see if you can change from 2mm (assuming two 1mm spacers) to 1.5mm. My guess is the amount you'd be able to move the cassette inward is very small, but might be significant. Most bike shops have a few spacer sizes on hand will sell them for $.5-$1 each IIRC.