Well... Once I got the cover off, I was able to run a signal line from the PCB trace to my oscilloscope.
The first trace below shows a negative pulse from the ECU, which bottomed out at ~ -5V. This was done with the controller connected to the engine harness, but the fan disconnected from the controller This test immediately resulted in an ECU trouble code, P0480 (if I remember correctly). I then cleared the code through my phone. Here is the trace which resulted in the ECU error @ 126F:
Next, I shut down the engine, reconnected the fan, and turned the AC on (so I would be sure the fan was supposed to come on). By this time, the coolant was up to 151F, and there was no ECU trouble code present. Here is that trace:
Next, I shut down the AC, and grabbed another data point:
I observed the positive pulse width widen to approximately 80%, and then all of a sudden, nothing. It looks like I burned out my oscilloscope in the process... Not really sure why (supposed to be good for +/- 20V), but I was looking for a reason to get the newer extended range (120V) version anyway.
So, it looks like the pulse from the ECU varies from -5V to +12V, at about 100Hz. It looks like the ECU is looking for a positive pulse, which is likely tied high by the fan coils themselves. I am thinking my fan is OK.
With all that being said, I guess I will have to pony up and call my local GM dealer to replace the stupid controller. I was unable to find the controller online, and AutoZone was no help either. They looked at me like I had 4 heads and their computer only came up with only the aftermarket cheapy temperature controlled relays.
Anyway, I hope this helps those tech-heads out there in the future.