This is not my area of expertise. I've seen a significant decline in aftermarket radios with the introduction of CAN. Just looking at the factory wiring diagram, the radio appears to be central to several functions.
For example, the steering wheel controls communicate to the BCM that communicates to the radio module. It is highly unlikely that the BCM will communicate with a non-factory radio.
I also see the following other modules connected to or communicating with the OE radio module, if equipped:
Electronic Brake Control Module
Telematics Communication Interface Control Module (OnStar)
Auxiliary Radio Control Module (backseat audio)
Auxiliary HVAC Control Module (backseat HVAC)
RSE Module (rear seat entertainment... DVD)
All this being said, I could expect to see several communications DTC's in a car with a module missing / not responding.