I currently have 3 Guppies, and 3 Black Lyretail Mollies in a tank together, and there has been no problems what so ever, they pretty much stick together and the Males are to busy breeding I sometimes see one of my female Guppies chasing the Mollies around but that is about it...But I do have a problem with my Pleco "Fred" chasing my Male Molly!!! He will even chase him to the top of the tank!! and its the only one he chases!
if u wanted to know my blue calico platy mated with my orange balloon molly (i also wrote a topic asking for help!!!) so i surpose the answer too ur question is yes it must be possible and i have heard that swordtails often mate with platys and that they have simarlar getnetics lol