I believe the point was that the bullhead may become an issue, not the knifefish. Xenomystus are the least aggressive notopterid I can think of, I've kept them with decent size tetras and never had a problem.
Depends on the type of Bullhead he has. Bullheads grow anywhere from 8"-12" Catfish are pretty aggressive eaters, so it would be something you want to keep an eye on.
Cool I appreciate everyones help. I was wondering what would be some good hiding places I could make in my tank for my knife fish. I Would like to know what hiding spots your knife fish use and if pictures are possible that would be great. Thanks
There are plenty of decor that you can find at your LFS that are designed to have caves and hiding places. I have four in my tank right now, plus another decor that some of my slender fishes (yoyo loach, bichir, spiny eel) have entered through the drainage holes on the bottom.