Were you finally able to boot your system without a video card?
I needed a box with no video, so after checking the manual, I bought the same board. As you state, the system doesn't come up without a video card.
Nope, after a couple of e-mails to Intel support I finally got this answer:
Where the TPS states:
""For use in embedded applications, the BIOS has been designed so that after passing the POST, the operating system loader is invoked even if the following devices are not present: Video adapter".
This is true in terms of a third party discrete video adapter, but only when the processor is a Clarkdale (Intel i3/i5 CPU with graphics integrated), so it has graphics and therefore will not need the discrete video adapter. Your processor however is a Lynnfield (Intel® i5/i7 CPU without integrated graphics) and therefore does not have integrated graphics, which is why your system will not POST, as our motherboards do require a graphics chip (integrated or discrete) to be able to pass POST.
I absolutely couldn't agree with such phrasing in the manual, and after annoying the support guys some more they promised to send my comments to their technical writers.
I'm not pleased at all about my purchase, but what can you do... I bought a second-hand low-power pci-e video adapter in the end. (asus/ati x300-se).
Thanks for the update.
Just in case anyone's interested: we tested a DP55WB board both with a core i7-870 and i5-750 (no video support) and it seems to behave as stated in the manual (2 beeps pause 2 beeps and then normal boot).