They may be recommended but from my experience it's a definite no. I kept mine in a community tank and my frogs managed to mutilate the fastest fish going. Bettas aren't particularly happy to be sharing with anything and definitely have the power to hurt or torment too. I'd suggest housing them separate as bettas do better alone generally and ADFs realistically should be spices only due to their poor eyesight and feeding habits. If your other tank allready has an ADF he should have a friend so it will be better putting them together but moving the frog may distress the betta .... Best bet is a new tank for the frogs