Hello Matt,
Pretty sure there is NO Option ROM, vBIOS and INT10H. Why INTEL for GOP uses VBT is point of debate. Probably just reduced functionality up to 1280x1024. So they have VBT to support BIOS phase GOP GFX. Only!
But I am also 100% sure neither GOP, neither VBT survives post BIOS phase. It is out of mind to use VBT for WUXGA, or 1080p, or 4K displays, don't you agree? The detected GFX I/F are passed to Linux as Run Time info (via HOB). Then Linux brings from scratch GFX, using its own, modern I/Fs. And ports appropriate drivers to existing GFX info from HOB.
Zoran