Way back, I ran a Seymour Duncan Quarter Pounder (passive) and and EMG humbucker (active) in a Tele and it not only worked well, it worked really, really well. Probably just dumb luck as I knew nothing back then. As for shielding a cavity, I can think of no good reason not to do it, unless you think you're going to screw it up. We all have guitars that play ddead-quiet (so we think) until we end up someplace where we start getting interference. Why not shield?