So I was able to find another PoE injector around the office, and the good news is that the Oak-D camera does work with this one, so that rules out damage. I'm still confused why the original injector would work a at the start but then seemingly quit.
The original PoE injector does have an indicator LED for when a PoE device is connected, and it was not illuminating suggesting that the devices were not getting along. (this was confirmed by probing VNEG and VPOS on the PCB and seeing only 0.3V)