Yes they can :)
I have a male plakat in a 20 gallon with four female guppies (not fancy), five micro rasboras, a few snails, and a tiger pleco. They get along really great, except the first week the male nipped at the guppy with the darkest tail. That has been the last of the fighting. The guppies know the male is boss, he has the upper right side by the heater and driftwood claimed.
Some people have a sorority, which is when 5 or more female bettas are kept together. A sorority can also be in a community tank. I plan on getting 6-7 pygmy cories for my sorority, but people have suggested guppies, mollies, bloodfins, tetras, etc.