I was wondering something similar a few days ago, but was worried as on google searching, there were suggestions that sea monkeys might be too big for bettas' mouths and they could choke, since sea monkeys are engineered to be bigger than normal brine shrimp. No idea if that has any fact to it though.
Found out that see monkeys are fresh water animals, so they have to be different. Maybe if they are freshly hatched they wouldn't choke? I think I'll give it a shot. They are easier to find than brine shrimp any way.
thanks for the heads up!!!