All crabs, let me repeat that, all crabs are opportunistic feeders. They will eat what they can get if they are hungry. Always hard to know if they are hungry but normally with our efforts to keep a pristine environment with little decaying matter, and the constant vying for food between all the creatures, IME sooner or later a crab is going to do something you don't want it to do.
If you are comfortable with keeping your tank more natural and letting nature take it's course well then the crab can stay. If you are more like me, I think crabs are evil creatures, banish it to your sumpfuge or back to the LFS.