ive had a balloon molly and a dalmation molly in with a male betta before and they didnt bother eachother, but then again...i guess it depends what kind of attitude the betta has too, my betta doesnt bother anyone, i even have him in with a female betta and they dont bother eachother, maybe hes a wuss lol..
but u could always try puttin them together and watch them and if somethin happens then remove them into another tank