Well it depends on the cory type and then of course the Betta. If it's just one Betta girl or boy then yes, I'd say you can most likely pull that off. But if you want a Betta sorority then I would be much more tentative, the girls would already be in stressed out mode since they aren't meant to be with each other naturally, they tolerate each other and that's it. So that's already lots of stress right there, plus a Shark chasing them on top of it....that makes me nervous lol.
For cory's, I would go with some of the bigger ones, I don't think Corydoras Habrosus or Hastasus would be a good choice, but sterbai might be good, Emeralds and Panda's/Skunk's, those type would probably fare better than the smaller ones.
Leopards: 1:4 Hawkeye, Luna, Astrael, Dorian, Cullen