If the voltage flows through the HUB, the test firmware will confirm it. The SSC itself receives the packets from the (modified) ethernet cable. The content of the packets are deciphered by the software running on the PIC. If the jumper is closed, the PIC modifies its internal storage to configure the string. If it is open, it translates those packets to something the nodes can 'understand'. This is all done at the SSC level, not the HUB. Having the test firmware running on the SSC is not going to break anything, but it will tell us if the string(s) are receiving the power they are supposed to. That would be one step forward, getting us very close to having some (controlled) blinking lights over there. The turnaround to just get there is a few minutes, worth it when we don't have direct access to the system itself.
If it works, then yeah, there might be other hurdles we will have to go through to get past the passive HUB. If it doesn't, we will zero in on the power injunction.