I won't admit to being a driver guru, but at best I might be able to help you to a solution.
I would think that as long as the drivers themselves are capable of recognizing the APU, they would most likely do so. I suggest this based on my experience with modems. As long as the drivers are "similar", then they are generally able to communicate with one another, though not in the best relationship possible.
I can in no way back this theory with any facts or evidence or really anything than say take it with a grain of salt.
Can I put in this way: in nForce2, the MCP-T actually communicate between the CPU, APU, and the ALC650 CODEC, so when the audio input is detected, the signal will be directed to APU, as APU should have the priority to process the audio signal. So, even if someone uses Realtek driver, as long as the driver itself doesn't care who (CPU or APU) process the audio signal, it'll just do its job and send the audio signals to the DAC and output them. Now back to the original question, could Realtek driver utilise nForce2 APU? I ask this question because I read from else where that someone is suggesting a guy who has nForce2 audio driver problem to use Realtek driver instead. So I would like to know if there is any possibility that this will work, and does this affect system performance or not?