Not if you really aren't copying the stuff to RAM. Rememer its not ROM you are looking at but the ROM shadowed into RAM. So its possible that you are checksuming the contents of RAM that has not be initialized. That would produce the results you see.
Have you looked at the area in RAM where this stuff is supposed to be?
I'm not near a machine that I can look up the command line but use 'hd' to look at the contents of /dev/ram starting at 0x0c0000 and see if the next 64k are really what you think they should be. You could also might use 'dd' and then 'diff' it against your vbios image.
It seems that the content on 0x0c0000 is not the same as the vgabios Only the first (between Offset 0x00 and Offset 0x7f) words are the same. The rest differs from vgabios (Offset 0x80 - 0xFFFF). That is the reason why X detects a valid vga-Bios section on Offset 00 and 01 (55aa) and the rest fails.
Now, I will have a look why this happens. Any hint?
-- Richard A. Smith