How big do they get. Will they go after sleeping fish for food. One of my gotten very big compare to my others. Its like his juice up... .I only saw him eat blue chromis not sure he caught him or was eating him after he die.
I don't have hermits in my tank (they steal food from LPS). But I am not sure I would worry about them killing a fish. I have a very large hermit (shell is larger than a quarter) in my daughters 28 gal tank, and there is a mandarin 4 chromis and 2 clowns. Never did I even see the crab have an issue with them. I would not worry.