How do you know that the video drivers are not seeing or interacting with the video card?
Because I've read the logs (Xorg.0.log, syslog,dmesg) and I've manually removed and reinserted the nvidia kernel module with maximum verbosity to see what it is finding.
Since the output only shows the one nvidia card (the fx 570 in the pci-e slot) and shows the pci-pcie bridge chip at the bus id of the pci slot in question:
07:00.0 VGA compatible controller: nVidia Corporation G84 [Quadro FX 570] (rev a1)
0c:02.0 PCI bridge: PLX Technology, Inc. PEX8112 x1 Lane PCI Express-to-PCI Bridge (rev aa)
I have another Dell Precision 690 that has an older 6200 based nvidia chipset, no bridge chip and everything works fine with 2 vid cards and 3 monitors.
I would have ordered the same card again, but it looks like cdw doesn't carry it any more.