Yes, if you overexpose slide film by about 3 or 4 stops, it will come out very clear. You certainly could layer a number of slides to composite an image of several items on white backgrounds in this way and then rephotograph the composite.

Layering negs is the approach to take if you have black (4 stops under exposed) backgrounds which would be clear on the negs. Doubling up a C41 colour mask would require some interesting filtration but (I suspect) nothing an enlarger couldn't handle. Requires little to no effort at all with B&W or (of course) photoshop.