I have around a 90 gallon display and 20 gallon refugium.
My porcupine puffer doesn't bother any corals and ignores snails, but I could definitely see him eating hermits, although I had a few that he has yet to bother and has not eaten them(saw him pick one up though and drop it, LOL), Let's just say I am not naming my hermits, once he gets bigger all bets are off(right now he is about 5 inches).