It will run as a 2WD if you pull the front drive components. Bear in mind that this puts more stress on the rear drive components like the rear diff. And it will not handle the same. Depending on what weight oil you had in your diffs, I would guess it will tend to push or under steer in the turns. But it will run.

As far as the wheels not turning on the ground, that has been true for several of my vehicles, especially ones with lots of contact area and grip on the tires. Often, the vehicle has to be moving for the wheels to be able to turn well. So I would not necessarily think that anything is wrong with your volcano. Of course, if your servo has enough torque, it will turn anyway. But then you are running down your receiver batteries fast as higher torque=more load=more battery drain.