Depends on the mobo and BIOS AND videocard AFAIK. Some mobos will attemp to boot, sceen will flicker, then go blank. Some won't even flicker as the mobo won't boot at all without CPU. Some mobos will attempt to boot and allow videocard BIOS to display, then nothing.
So, IMO, it depends.
So I would have to vote for both!
Cheers
Mick