Rotors being driven is not a requirement for VRS; pitch applied is. The rotors don't care whether the drag force is overcome by the energy from the engine (as in powered flight) or rate of descent flow (as in autorotation).
In VRS an induced flow from applied pitch is opposed by an upflow of air from a high rate of descent: the lack of airspeed localising this confused airflow to the disk.
With pitch down, you won't have VRS: but if you apply pitch with a high rate of descent and no airpseed, what then?
TT