I don't think it's considered traditional woodworking technique.. but there are all sorts of ways to utilize orbital sanders. I have alot of work experience using both the pneumatic ones, which are totally awesome and feel great in your hand, as well as the more cumbersome electric ones. I recently worked a job building custom vinyl fencing and we assembled the stuff with nail guns and epoxy and used those little pneumatic sanders with 60 grit on them to form, sculpt and blend all kinds of stuff. I spent a good chunk of time working at Warmoth as well and it is common practice to final shape out guitar necks after they've come off the cnc with an orbital sander there. I now do so on my own after I am done with my rasps and files. It just takes a quick, smooth and precise hand to keep it moving and flow with the shapes and curves of whatever you're working with. I will often hold the orbital and use just the edge of the disc to shape volutes and heels and so forth.

Anyway, whatever works for you works, I wouldn't get too caught up in tradition and what others might think is unprofessional. I have never done a carved top guitar, but I have thought about what you are proposing. You could not outright carve it with just the orbital, no way. It would take forever. But if you route ledges, or start with a rasp, or chisels or what have you, you could blend and shape to your final stage with the orbital. I would get some 40 and 60 grit discs and try it out. Let us know how you make out if you try it.