Crs are awfully pricey to risk as betta snacks. :/
They're also very sensitive. I've been researching them for months and am about to set up my first shrimp tank. (After it cycles of course).
Even if your betta leaves the adults alone, you won't get any babies. :(
If you want shrimp in the betta tank, go with something a little bigger. Amanos are a good choice as they are big enough to defend themselves. I've also had success with ghost shrimp and bettas.
Maybe look into setting up an appropriate shrimp specific tank if you're set on the crs?
they sure are lovely. I just ordered 50 S grades and my friend is holding shipping on them while i cycle the tank and even with the "family and friends" discount my picket book took a hit.