ACFs will eat anything that they can stuff into their mouths! One came with my tank, and I didn't know that until I innocently added 10 baby Cories. I managed to get him out and transferred to an unoccupied tank before he killed them, but he tried to eat 2. They got lucky, I nearly had a heart attack. I then did some research on the creatures and discovered they will eat anything and everything. The only thing that stands a chance are much larger tank inhabitants, which may pick on him. They will even try to eat their own kind, unless they are about the same size, then it's just "iffy."
I don't really recommend them, there are no redeeming benefits. When I traded in the huge fish that came with my tank, I wanted to trade him in, also, but my husband thinks he's cool. So, I have a 30 gallon that he has all to himself, and I'm stuck caring for him. He seems dumb as a brick and doesn't do anything. I take good care of him, of course, but I would happily give him away tomorrow if not for my husband.
African Dwarf Frogs are a whole different story, however. They are harmless and peaceful. You just have to make sure your other inhabitants won't harm them. I would imagine the Jack Dempsey and crayfish, at least, could pose a problem. J.D.s should really be kept in a species tank, not a community tank, but that's a different story. Peaceful community fish that don't get large enough to eat an ADF would be good tank-mates for them.
Hope this helps!
Hobbyist for many years.