best i can tell from the pic the crab is a stone crab ......likes to eat meat ,snails ...i was was always told that crabs with sharp claws not good crabs with blunt claws (emerald crabs for exampl) good to have
i dont know about the hermit ...most just scavange so i would just keep an eye on it ...cant remember ever seeing anyhting or reading anyhting about any hermit that actively hunts ...