That is an interesting idea. To answer your question, yes stepper motors are used to drive the rotating platters.by Brenon - Polar Machines, SCARA, Robot Arms
Here is a new polar configuration that we just got working as a proof of concept. It has two platters, one rotating on top of the other, but with stationary motors that result in a dead simple drive system. Video here: Printing: Motion is smooth and the platters can move surprising fast. Little or no frame vibration/shaking since the start/stop motion is rotational. CNC MIlling: A lot of thisby Brenon - Polar Machines, SCARA, Robot Arms