Hi Fishy,
I sure can't say I KNOW, but I personally have a blue crawfish (the florida variety) and crystal red shrimp in a 30 gallon and they all get along fine. The crawfish seems singularly disinterested in the shrimp, and they eat side by side. Although, if one of his antennae touch them, they whiz away in terror.
I'm not sure if it's a personality thing, but that would really be my guess. Everything I read about them before buying went on about how aggressive they are, but mine seems particularly unaggressive compared to other crawfish I've had, but this is my first Florida blue, so who knows?