I used to keep a male betta and a few African Dwarf Frogs (the small, non-aggressive frogs) together. They all got along well. I had a bit of trouble when it came to feeding though. Be careful, the pet store will try to sell you the processed frog food in a little container. The processed stuff can cause all kinds of health problems. They need frozen bloodworms to be healthy. It's not much of a hassle at all. Most of the big pet chains have a freezer section. About half a cube is more than enough for three frogs and the pack will last for months. The only issue with this is, Mr. betta is going to think he's gone to betta heaven lol. They love the stuff and will over eat on it every time. The good thing is the frogs only need to be fed every other day.
Just something to think about . It could be solved easily but just netting the betta when it comes time for the frogs to eat (they take awhile, I don't know how the poor things survive in the wild).