The crayfish will try to eat anything it can, so with a few of those being bottom dwellers, particularly at night, the odds increase that the cray will at least injure them. When the cray molts he will need a very tight-fitting cave where only he can get in/out of, otherwise the others will kill/eat him.
(I've had my cray with WCMM, danios, curviceps, dwarf puffer, kribs, guppies... he has at least nipped the fins of all of these and has killed/eaten many WCMM, danios, and guppies. It seems the smaller the fish the easier it is for him to make a meal out of it, but he done damage to the others,too.) Just something to think about.