I didn't put them in there, but I have snails in the sump. It just happens. Every time I find one in the overflow or return section, they get put into the fuge. They definitely help keep the sides clear enough to see how the macro algae/pods are doing. You'll probably want to remove any smaller ones you find in the sections with pumps. They tend to clog up impellers.
I have a ton of snails that just crawl down the overflow and a peppermint shrimp that was banished there. No idea what that shrimp eats but has lived in there for months