I've removed one by finding his 'home' rock just by keeping an eye on the tank and then removing the whole rock and shaking him out into a bucket. I've also had luck with a jar propped up against the rockwork with one of those sinking algae wafers in it as bait. I wouldn't worry about the hermits. The evil crab will fill up on the bait once in the jar and if you do loose a hermit that sucks but you're better off making sure that crab is out of your tank.
__________________
|