Yes but the fry will need to be moved to a larger grow out tank. I suggest you do a good amount of research and preparing before you attempt it. Takes a lot of time and $$.
Matthew The Fish King
Plus bettas r generally hard to breed because some will usually not get along
I'd imagine you'd have a hard time selling Betta fish because they are so common and cheap. Probably would end up costing more to breed and house than you'd be able to make in return. If you are serious about breeding, look into Discus or something that sells.
A 10 gallon is usually recommended for breeding them, as the fry will have enough length to grow for the first few weeks. Of course, the male and female can't be left in there for any extra time, and there's a good chance that one, or even both will die. They will sustain serious injuries. You'll want at least 1-2 40 gallon breeder tanks and 100-300 jars for the aggressive babies. You'll want to heat the room they're in enough to keep temp of their jars 78-82°. This isn't a cheap task by any means.