It really depends on the fish. Both the betta, and the others. I have heard of many males and females being okay in a community tank. I have also heard of many males (and females) becoming to agressive. I have a personal experience where my platies began to nip my female betta to shreds, and I know it would have been worse if I had placed a male in there.
If the betta has a friendly personality, it might work. But bear in mind you must watch for damage on the betta and on the other fish. You also need to make sure the bettas are eating, and that the platies do not steal all the food away.