If it's any consolation, looking at the two pictures side by side, I can see the Rod Stewart in that pic of Gray Carlyle.
One other one I've had a hunch was based on a real personality was General Alexander Kerensky, whose picture in Liberation of Terra I looks very much like his real-life namesake, Aleksandr Kerensky, the leader of the February Revolution in Russia. Just remove the hair (the real Kerensky was not a chrome-dome) and they are very close together in appearance.