If its just the small shrimp, IE not the one that punches "mantis shrimp" your golden. Mantis shrimp will kill everything. and i mean evvveeerrryyyytttthhhiiinnnnggggg. Like nothing will stand a chance. But be wary of those horse shoe crabs, they get massive so you need to have a long term plan for the guy. Eventually hell get so big hell knock over rocks and possibly hurt the tank. "i doubt that" but it could cause problems.
Ive kept them in the past and when they got to big I would always ask around my lfs and shoot even the local aquarium. But remember that might not be an option. And NEVER set it free. I am pretty sure that is illegal. But best of luck!
I think Caleb M is dead on right. People confuse pistols and mantis shrimp. I can't see a pistol shrimp hurting anything. They're constantly popping with their goby partners around and they seem to be fine.