Absolutely! Snails are very much like slugs, except they have an external shell. Most slugs, OTOH, have only a very small remnant of a shell, which is internal.
It has been my experience that, when I fail to keep the snail population under control, the slug population decreases dramatically. When I keep the snail population under good control, I see more slugs around. I don't know whether that "balance" between the species occurs anywhere else, but it is what I've observed in my own yard over the past 30+ years.
Snails will eat just about anything that's green. I've even had them attack cacti that had really wicked thorns, so I'm sure they'd delight in dining on tomatoes.