They do have small teeth. They can be a little aggressive sometimes. I recently set up a tank only for blind cave tetras and they can go crazy everytime I feed them.
congo tetra's are my fav community tetra fish. very colorful, gets to a good size. tho they show visible tiny teeths. but are really harmless. have never heard or had experience of them nipping other fish. however, they do nip on plants. pretty cheap and beautiful.