Is there any advantage to preparing the tire bead with sealant during installation on the rim I am on a hard tail 29er and this is my first time going tubeless. I will be mounting 2.4 Maxxis DHF to a carbon 35 mm rim. 

Where I am going is remote, quite rooty, and there are lots of technical small-rock gardens as well as broccoli and smaller rocky trails. 

My plan is to go with lower pressure, maybe 20 psi. But I don't want a burp in a rough descending off camber turn and then have to pull out a spare or have to try to get the tire re-seated.

I'll be using gorilla tape on the rim instead of the 'official' tape, no diff there and save a few bucks. 

I saw them apply a milky coating the last time my car tires were installed and the shop guy said it was a water soluble latex to help bed and seal the tire to the wheel. 

Most people use a mild soapy water to wet the tire when mounting. Given that 
I am using Stan's or Slimepro, would it help to apply a thin film of the solution to the tire bead when mounting them on the rim?

edit 1: What I did in the end

Before mounting the tire on the rim I watched the Slime Pro how-to video on YouTube
Slime Pro - Official How To Video

So, I guess that answers it, yes, it is recommended to use the sealant as the tire bead bedding solution as far as Slime Pro is concerned. Also, I tried that, exactly as shown in the video with a toothbrush and got my 'two loud pops' and a bubble free (perfect seal) of 2.4 Maxxis Minion DHF on a 35mm wide 29er rim.

The sealant, which is slippery and stays liquid actually for quite a while (definitely more than 5 minutes) seems to be excellent as a tire bedding solution.

I had a really tough time getting my last tire (2.35 Hans Dampf) on the rim. That one took forever to get on the rim (at least 5 minutes) and the sealant I applied to the tire and the rim stayed lubed until I was ready to air. Also a perfect seal and some good 'pops' when airing.

edit 2: What the local bike shops do

I inquired at 4 well-known local bike shops in the area to find out how they do tubeless mounts. All of the service departments said that they use the sealant (Stans Tubeless Sealant) instead of soap and water for tire bead mounting. So it turns out that no-one around here actually uses soap and water any more.
The soap and the sealant do not have the same purpose.  

The purpose of the soapy solution is to lubricate so the tire better pops (seats) onto the bead.
For some tires it is hard to get them on the bead (especially with a hand pump).     

From there the sealant in the tires is used to seal.  

Stans has some good videos
StansHelpCenter

tireinflatingtips


  Use soap and water to help the tire bead seat.   
  
  Do not add sealant until you’ve successfully been able to seat the
  tire.


I get the thought of have some sealant on bead.
But I will go with getting the best seat (soapy solution).
And that is what stans recommends.  

Other tricks are:
Shake the tires to disperse the sealant.
Lay on each side for 12 hours.
Run em up to 40 PSI and be sure they hold for 24 hours.
Some tires suck up a lot of sealant - you may need to add sealant.