I have heard of people using vibrating sanders for prep work, but I would think an orbital sander would spin too fast even for prep work, and you might end up damaging stuff you didn't want to sand. Might be OK for large flat areas like the roof. Try it out and see how it goes.

However if you used an orbital sander for wet sanding you'd get swirls like crazy, I would think. My .02 cents FWIW.