On most every site they say male bettas are usually impossible to keep with other aquatic beings.
This makes me sad because I have had excellent luck housing a single male betta with other fish. I had one with a silver molly and a small bumblebee goby... they got along really well. Even on site that talk about bee goby care they say not to house with bee goby with fancy fins such as a betta...
I think what it comes down to is temperament and how the fish are introduced to one another
Currently I have two female bettas and two snails... the second betta I just recently acquired and have the divider up until they get acquainted with one another... the only problem encountered so far is that they have never seen a snail in their lives before so they go 'snail tipping' every once in a while