Well, I've tried using a cheap scanner behind a 5x7 camera and I can assure you're gonna have a lot of fun. After many tests and hardware surgery, it produced some of the most awful images I've ever done. The hole process of making light converge to RGB sensors, using mirrors or who-knows-what-else, will actually deliver a raw image full of stripes, unevenness and all sort of bugs you can imagine. Of course, there's a lot software processing so the scanner can fulfill it's basic task of scanning flat work and it should be done again on every image you make.
Maybe under a enlarger things could work out better using some kind of ground glass so the image could be projected on the right plane and the scanner could act on its usual way. But just don't forget scanners need calibration,which is usually done automatically by its own light source hitting targets inside the machine.
Anyway... good luck!