Tried upgrading the firmware on my Adaptec 7805 to the latest and greatest... no change. 
Tried installing Fedora 14 as another test case... when I have the PCI passthrough enabled, the OS will not finish booting. It takes an extremely long time on the white "Fedora 14" bar, but never completes. The box never gets to the point where it brings up network interfaces, so I have no way to get in remotely and see what it's being hung-up on.
This problem is extremely frustrating given the amount of $$$ I've spent on the hardware, especially since I heavily researched the compatibility. Evidently PCI passthrough is not part of that.
Guess my next step is to try a different Hypervisor, which is unfortunate because ESXi 5.1 is pretty neat (aside from this problem)