I really wouldn't. I could imagine some people doing it, and probably having it work, but it really depends on the size of your tank.
Unfortunately, both rainbow sharks, and leporinus fasciatus are both pretty mean fish. The shark is more territorial, so it by itself shouldn't be too terrible is you got an angel.
The L.F. though, they can reach sizes up to a foot and are very aggressive. They would definitely at one point even beat up a rainbow shark.
If you had the angel in the tank first, I'd say your chances are best, but putting it in last would 'most likely' be trouble.
But who knows, as long as you had a big tank and a lot of cover, it may work. That is until the L.F. gets large.
