Hermit crabs have a tendency to kill snails for there shells. some have claimed success in putting in empty shells for the hermits to move into when they start to grow, but no guaranties. I believe someone has told me that sally lightfoot's are good algea eaters, and reef safe. HTH
I recommend that you avoid "red leg" hermits, which I believe are different from "scarlet" hermits. my favorite hermits have been the hawaiin zebra and the electric blue <----my most favorite.
I also would avoid large-bodied crabs such as decorators and emerald mythrax. I have had experience with both of those guys destroying polyp colonies and mushrooms. Especially the decorator. They'll pick an entire colony to wear on their back, and end up killing them.