That said, the board's activities seem to be pretty vendor-neutral so vendor affiliation doesn't seem like a big issue.
right. regardless of who we work for, we act in the best interests (as we perceive it) of the Foundation and of X.Org as a whole. board members are explicitly acting as personal representatives, not as company/vendor representatives; i would not vote for someone who attempted to get elected to further their employer's interests.
That would be an ATI candidate, in this case, as the other case would require one of the AMD GPGPU people to be involved (the same people who got you the evergreen ISA docs).
Don't think we have any X.org members from that group, maybe since you seem to know the AMD internal company structure so well you could talk to them and see if they have any interest in joining X.org or running for the board.