I know its possible to make a "supercomputer" with multiple Raspberry Pis, but is it possible to make the Raspberry Pi add to the current ram/cpu of a laptop running ubuntu or another os like OS X, or Windows?
No, it is not possible to build a supercomputer with Raspberry Pis (some people have made clusters as an exercise in making clusters).
No, a Raspberry Pi will add no meaningful processing power to a recent lap top.
Considering that a modern laptop is likely to have significantly more CPU and RAM than a RPi, I have to wonder if the effort is worthwhile? Not to say that it might not be possible to cobble something together, but it's probably not worth the effort. Most clusters use identical or at least similar hardware.