My beta tank is currently housing 1 male CRS. He survives fine, but hides constantly. My beta is pushy. He doesn't seem to bite(mouth isnt big enough), but he does chase him around. The shrimp is much faster than the beta. I feel bad, I'm waiting for my 10 gallon to cycle before putting him in there with a new batch of CRS.
If you want to do it, add tons of hiding places the beta cant get to. Some beta are pretty peaceful, but others can be super mean. If you see it attacking its reflection...it's likely not a good idea. At the very least the fry will get eaten. Mine seems to be middle of the road. He flares up when he sees his reflection...but doesn't smash his face into the glass like some.