I havent noticed my cleaner shrimp eating any snails. The few hermits I have ate some snails for their shells, but I have over 100 snails and 5 hermits, so Im not too worried.
I credit the dozens of stromatella snails in my fuge for why its so clean. They even live in the cheato. Somehow they got inside my skimmer, its kinda funny to see them in there.