it all depends on the betta. i've had two other bettas in my molly/platy/ADF community (not at the same time!) and they did fine, but my newest is having more trouble adjusting, he's calming down now but he was nippy and chasing for a while. some bettas do well in a community, some don't. i'd float him in a cup before introducing him, see how he reacts to other fish.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)