I believe the OP is asking about the presence of an "Imperial race" in the games, not necessarily the presence of Empire-building Men in the universe. As ZindroVokun said, Cyrodiil and the Legions would probably be predominantly filled with Nords, though I'm sure there would be more than a few Bretons as well (Hjalti himself was from Alcaire, though he pretended to be a Nord and gained the Nords' loyalty by turning them against the Bretons that they had kind-of allied themselves with when Cuhlecain became too powerful to fight alone). Cyrodiil, as the Imperial melting pot, would have been populated by almost equal numbers of every race, but the Nords and Bretons--especially Nords--would have been in the highest positions of authority in almost every case, especially in the Imperial City itself. I can imagine Altmer becoming more and more powerful in certain factions (the Mages Guild comes to mind), and even in a city like Anvil that is open to overseas trade and is near Summerset, but the other Elf races would probably have too much stigma to get around (the Dunmer, after all, are basically insect-herding heathens who worship Daedra and hate everyone that isn't Dunmer, so they wouldn't get far; the Bosmer are cannibalistic savages who live in trees and have no proper civilization, or at least so the Imperial revisionists would claim when they don't want to be reminded of Camoran or the later Usurper), and of course the Khajiit, Argonians, and Orcs would never be accepted in positions of authority (except for the Orcs in the Legion; they are, after all, great warriors, and the already-existing reputation and hierarchy of the Legion would allow Orc members to raise themselves up based on their merit and skill. The same is true for the other races, of course, but Orcs are much more likely to succeed in Legion life, and therefore benefit from the Legion's reputation in Cyrodiil as a whole).