They should be fine as shrimp are a bottom cleaner and often stay out of a bettas way. People have combined ghost shrimp, african dwarf frogs, and have rarely had problems.
It can really depend on the fish. I got some ghost shrimp to put in one of my tanks but my betta thought they were part of the menu. Needless to say I am not going to do that again. My bettas actually hunt down small snails for a snack.