I have had a 5 gal tank for about 3-4 months now and it consists of 1 Betta, 3 Glo Zebras and 2 Neons. There doesn't seem to be any problems. Even if the Betta thinks about it the Glo fish Zebras and Neons are just too quick for him.
He likes to spend his day going down to the bottom, swim...