Hi F.:
My kids have never attended UNLV preschool, but a good friend of mine had her daughter there, and they absolutely loved it! As for starting your son right now, I think there are benefits and drawbacks.
Aside from the germs, you want to make sure your son knows that you aren't making him "go away" just because you are going to have a new baby to take care of. Kids have a strange way of thinking everything is their fault, and I've read that putting them in preschool so close to the birth of another baby can send them the message that you have a new baby around and don't want them there anymore. I do think that at age 3, there are tremendous benefits to putting him in preschool. My son is 4, has never been to preschool, and I can see a big difference in him than other kids. The attachment he has to me, simply to go to Sunday school at church was a real eye opener to this problem.
I think that since you did get accepted at the UNLV program, it would be a good idea to attend. I've heard that it is sometimes difficult to get in there because of such a long waiting list. And as long as you make sure your son knows he is very special and just as important and loved as the new baby, you should be fine. Good luck, and congratulations