The VBIOS should not care if the BIOS has legacy enabled or not. The only thing that matters is how you installed you OS on the hard drive.
Okay so I'm not sure what's happening here. I have integrated graphics HD 4600 and a GTX 560 ti. Now once I installed Windows 8 as legacy boot but later converted it into UEFI using gdpedit. Now if i disable legacy boot the screen remains blank and to restore it back I have to remove the graphics card from PCIe slot and plug the monitor to motherboard. But if i have both the boot available the graphics card doesn't have any problem. Any idea?