yes, it is a gamble, as Lupin said. i had all three of my male bettas with at least one snail in their tanks (10 gallons) and had no issue with nipping. i'm pretty sure i just lucked out on some uber mellow betta boys.
perhaps try it, but ask the lfs if you can return it if the betta harasses it. around my neck of the woods, most smaller lfs have no problem with that.
unless you want to become a ninja with the gravel vac, lol, don't get more than two.