They do well with hermits. Thing with emeralds is you won't see them much. I put one in two months ago and I've barely seen him. Saw him yesterday so I know he's alive!!
Emeralds won't really bother anything, I've had mine for a while now and he's been fine with all my shrimp. All he does is put his claws up in defensive mode if a fish swims by but he's never attempted to attack one.