Can Mac Pro use the Nvidia NVS 440 card?

The only video cards you can use are those available from Apple specifically for the Mac Pro. Third-party cards do not have the required ROM for booting an EFI-based computer and will not work on the Mac Pro.

If you create a Boot Camp Windows' partition and install Windows along with the appropriate Windows' video drivers for the card, you should be able to use it, but only in Windows.

If you have more than one video card installed in the Mac Pro they must both be either NVidia or ATI, but not mixed.

I think the BTO ATi and nVidia Quadro cards both have 2x dual link dvi ports, which would allow you to use the monitor at full resolution and refresh rate I believe.

I'm not sure if the NVS 440 will work, but it's unlikely.

There were a couple threads on video cards and displays. There have been attempts to use PC cards and flash them. Macs require 128k ROM for EFI and BIOS firmware to work.

The Expansion Slot Utility.app will come up any time the system detects a new PCIe controller, only it may not be visible if the screen is black and no video output - people have tried to work around that using one monitor on another video card and then changing on restart.

Two cards, both with SL support to one monitor doesn't sound promising (and there is at least one thread on SL support if not more, in the Displays section I think).

Maybe things will change as the Mac Pro line matures. And of course there are now "talks" about Intel acquiring Nvidia.