Can you use USB Video as the only output?

I’ve been reading about [url=http://www.usbgear.com/USB-Video-Card.html]these things[/url] for a couple of days now and I’m wondering if it’s possible to use this as your only video “card”.  My guess is that the motherboard is going to complain that it’s missing a display device, but I was wondering if anyone knew for sure.  I’d love to use one of these for a headless server and save the precious PCI-e slots for more important cards.

Anyone?  Thanks in advance!