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.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams