I've tried several types of hermits, and some seem to be more snail safe than others, but I have always lost snails to hermits. I've even seen the different types of hermits gang up on a seemingly perfect healthy snail, kill it, then fight over the shell. I avoid hermits in my tank, and have not added any more after my initial bunch... Just kinda waiting for them to die off.
You should look into getting a variety of snails (nassarius, trochus, cerith, astraea, mexican turbo), an emerald crab or two, one brittle star or serpent star, and a pair of shrimp. That's a pretty well rounded cleaner crew for a tank your size, IMO. Just don't get a sand sifting star. Brittle or serpent only. And no green ones! They like to snack on fish.