im my experience, its not just the betta that you have to watch out for, when i first started out i had a male betta in with 7 guppys, aswell as someother stuff, they are not important, the thing is that the guppys killed the betta, stripped him completley of his fins. i put the guppys in a different tank on there own so because they were also attacking other fish. a bit later i bought a south american puffer which can be nippy so i thought id put him in with the guppys before i put him in with the other fish. the guppys atacked him, not the other way around.
basically what i am trying to say is DO NOT UNDERESTIMATE THE GUPPY. They are nasty fish and i will never keep them again.
hope this helps, although obiously it may of just been the personality of the guppys as all fish are different, imo i wouldnt try it.
mine don't eat snails, whether or not other ones do i don'tknow