Yep ADFs are popular to keep with bettas due to their small size, relative easy upkeep (most people feed their bettas bloodworms a lot anyway, thats what ADFs eat) and that they are the only small creature that bettas are unlikely to attack.
Don't get them confused ith ACFs (African clawed frogs), these grow biiig and will kill your fish! Go and have a looky in the Invertabrates and Amphibians bit.