It depends on your setup for your betta.
For example, if the tank is filtered (As in running water) I don't suggest an ADF, as they prefer still, brackish water.
They're also TOLERANT of salt, but don't particularily need, or enjoy alot of it (but your bettas sure do!), so that part is up to you.
I have a female betta and two ADFs in a tank (They're extremely low waste producers).
Be advised there is some nipping and bullying for the first day +. Your betta will give chase, flare, and nip, but unless there's some serious agression going on (cornering, really ripping into the frog) you should just watch carefully and let them adjust to each other.
My female hardly notices them now.
Beware that your frog might instigate fights by nibbling on Betta fins (I think it's just a case of mistaken identity), but other than that, they will get along just fine.
It's all about knowing your bettas personality - Are they unnecessarily aggressive towards anything that comes near your tank?
If so, ADFs might not be your best choice.
But if your betta is an average joe, aggression wise, they'll adjust and cohabitate perfectly.
Temperature for ADFs are in the mid 70s, which matches bettas fairly well. I've found my ADFs prefer 78 degreesish, over anything else, and are most active at this temperature, so if that's good for your betta, I give it the go ahead.
