I think that hymenochirus is a type of ADF. Are his hands webbed? If so then he will be a little guy about 1.5 inches, if his hands aren't webbed then you have an ACF and he will get bigger around 4 inches. Sometimes fish stores label the two different frogs incorrectly.
Some people say they are good to house with bettas, but I would never do it. My frogs get aggressive around feeding time, so odds are they would bite my bettas fins. I've also read that a lot of times Bettas will go after the ADFs. If the tank is large then it should be fine, I'm not too sure how much 11 liters is so I don't know if that is large enough. But you could try to house them then if you see and problems seperate them. Just make sure your frog does get to eat, when they are housed with other fish sometimes they aren't able to find the food fast enough and will starve.