Shrimp are trigger food. Wrasses and gobies are the cleaners of triggers. Shrimp are a feast...no shrimp(and probably a good idea for no snails or crabs) for a trigger tank. Granted some triggers don't have an attitude and won't harm them, but this is a risky call. Carnivores are usually not the best tankmates in a reef setup.
By that theory, mantis shrimp and snails live in the same waters. I dare you to put a snail(or crab, or shrimp) in with a mantis!! Mmm...Mmm, lunch. Parrotfish live near coral, but don't put one in your tank. Everything lives near it's prey, that is how it becomes prey.