I knew guppies could take some salt, but I didn't know they could take full marine conditions. If they can, may be worth a try. But the Snails themselves are actually tidal snails. They live on tidal flats, and I am not sure they can live in full marine tanks. The eggs are usually laid on wood or rock, so you take the rock or wood and put that in the marine tank to hatch out.
If it is possible to keep Nerites in marine conditions, they would no doubt need some time to adapt. They spend a fair bit of time in the wild out of water, when the tide goes out, so in habitat they are only submerged for about half the time. It's why they can sit on the tank edge for hours and not dry out. Be great if you are able to manage hatching some though. They're such pretty little things.