I have 6 cories in with my females. I used to have guppies in there with them for about 2 to 3 months but removed them when i started getting more females...I had no trouble with the girls and guppies. (about 6 of each)
i was just in thailand, and all over the place in the streets they have these large pots with siamese fighting fish and guppies in them, together. they seemed to be doing great! one i saw had 3 female bettas and about 10 guppies.