When I wrote "VPP controller" I was referring to some unknown Tesla software that exists only within Tesla corporate that processes the CAISO/CPUC/PG&E/SCE triggers for an ELRP event and then dispatches commands (charge, standby, discharge) to the Powerwalls that are opted-in to the VPP program.
The only visibility that we can see is what is the VPP tab in the Tesla app that covers the event timeline, what our equipment is doing, how many fleet homes there are participating and the aggregate kW charging/discharging.