I used to use an Olympus OM-1 quite a bit with a couple of nice Tamron lenses. You would buy a mount dedicated to a specific manufacturer of the body. I've decided it's time to go digital beyond point and shoot type cameras, and would like a DSLR, but would like to be able to mount these older lenses. FOV multiples aside, can I buy a mount and use them on any Canon, like a Rebel, do I have to go full sensor? Thanks.

The mounts you're talking about provided a mechanical connection between the lens and the camera body, but not an electrical one. There may be mounts for the lenses you have to connect to a modern AF AE dSLR, but they won't autofocus and they won't work with the automatic exposure system either. You may spend a lot of time and effort trying to make them work, and then decide it wasn't worth the trouble.