I know this is an old thread... this might help for future people thinking of ghost shrimp. I mentioned in another thread that I put in 9 ghost shrimp in our new betta tank (I finally got an accurate count yesterday) first and then added the betta. We have a clearly larger, dominant ghost shrimp and then varying sizes... some are relatively small. All have made it. The key seems to put them in first then add the betta and the betta won't see them as invaders into his realm.
As for escaping... uh, yeah... particularly when you're trying to acclimate them to the water in a tupperware bowl. They will absolutely try to get out so fair warning. I had to rescue them 3-4 times before I finally got them into the acquarium.