Not safely as a longterm arrangement. As with any animal there will be individual variations, and some clown loaches may be more enthusiastic snail-eaters than others, but as a general rule you shouldn't plan on putting any snails you want to keep alive in with a clown loach. Small snails will be lunch, and even small clowns will peck away at the flesh of bigger snails. Bigger clown loaches can munch right through the operculum on even very large snails. I have read some reports of MTS (Thiaridae) populations being possible to keep with clown loaches for a couple of reasons: the snails will reproduce quickly with sufficient food and they usually stay in the substrate where they're harder to find. However, I have never tried that particular combination myself, so I don't know the exact conditions needed (substrate depth, etc.).