Yes they can, however you have to make sure it's the right fish. Some fish can be fin nippers like most of the Barb family, most torpedo shaped Tetra like Neon Tetras are fine to be housed with. My Female Betta Sorority is in with 7 Neon Tetras, 6 Dwarf Cory cats and a Bristlenose Pleco. You just have to be careful about nippers and then of course some betta's can't handle being in with others and might stress them out so you have to watch for their personality as well.
RJ (H. Lifalili), Acara (EB)
Ghost, Tuxedo, Trip (Angels)
Leopards: 1:3 Hawkeye, Luna, Astrael, Dorian