I had an emerald mythrax until he recently passed away and a good assortment of both scarlet and blue-legged hermits. Sure, I lose a nassarius or cerith snail from time to time, but the benefits of the crabs cleanup ability greatly outweighs the minimal loss in my opinion. Plus, I happen to like the little buggers..I find them rather amusing!
Another thing to consider is that if you were keeping land hermits, you should provide some extra shells for it to move into. I feel it's no different with the aquatic guys. I know that many of the LFS's I've seen have tons of dead snail shells in some tanks (usually due to inappropriate acclimation) and would probably be happy to make some spare change off them.