A brief update on my situation.
I got an IDE-to-SATA converter installed on my SATA drive and was able to install the WHS2 v2 on it.
Once I got the OS to boot up, I installed the driver found on the NVIDIA site and the SATA/RAID controller was detected as expected. I connected a spare drive and it was also detected without any issues.
So even though the installer didn't recognize the M1573 SATA/RAID drivers during intial setup, the actual WHS v2 OS itself does.