I've read that it's possible, but it's a case by case scenario dependant on the personality of the individual fish.
You can try it, but monitor them, and have a place to separate them to, if it doesn't 'work'.
I've actually been considering this route - I have a 2 juvenile girl gourami/rainbows tank - that I'm intending to attempt to add a king betta to. (but not for another week or so) - the betta is still in quarentine - and, I'm still working on (planting) the tank to make it a bit more 'private' for the fish who require solitary time.
TheJewels... 20 g H plantedsorority - 4 princesses & 3 zebra otos
Ladies of Camelot - extended visit of Rome - 7 pretty girls & 7 cories - 20G Long.
Gawain - hM (2.5 g planted tank)
Lancelot - hM (5 gallon tank)
Roland - CT (5 g)
Galahad - deltatail (15 gallon divided)
King Richard the Lionheart- king betta (12 g Camelot)
Tristan - VT- (15 g divided)
Robin of Locksley (20g H w/threadfins/neons)