I went to cake decorating school and actually did okay, but constructing an agitator cake would be a challenge. My first thought is to rule out fondant. That just seems a recipe for disaster, pun intended.
So which agitator design would translate most successfully into a baked good? Figuring that the entire cake is edible and cardboard is not used to replicate column vanes and base skirt fins, my vote would go to the Penta-Swirl. Seems like something that could actually be carved from basic cake shapes easier than fashioning a GE Ramp Activator or Whirlpool Super Surgilator (with wings!).