Actually, I have two mini african clawed frogs.
I bought them thinking they were dwarfs, but apparently they are not. Though, in the 8 months ive had them, they havent grown a bit. There are genetic ways to make them stay small, and i unknowingly bought into it.
As for the relevance, i have had both of them in a tank with my male betta, and there were no mishaps. this also goes for the personality of your fish, and the frogs. My betta doesnt bother anything in his tank, as long as they know hes big boss, anything i put in his tank is fine with him. Ive never even seen the frogs go after him, they only respond to the smell of food, which is basically the frogs strongest sense. I do know they can latch on when they want to, as i sometimes feed them with a pipette, which is a type of syringe, and they clamp on, and wont let go til you shake em a bit!
That being said, mine ARE AFC's and not Dwarfs. Dwarfs are much, much smaller, and are much more delicate. A good way to know how your betta will react to something that small, is to try ghost shrimp. My betta wont touch em, even watches as they take food from him. Some bettas will attack the ghosties, but are fine with other fish or frogs. It really all depends on their personality. My betta even loosely schools with a few Rosy Red Minnows i have.
a big problem with having bettas and frogs in the same tank is the frogs ability to only eat whats right in front of them. They usually begin to starve, because the betta will grab all the food. Which is why i feed with a pippette. Though with time, my betta learned to not eat the sinking food, and only the top food.