That's all very superficial. Look a little closer, read more in game books..you'll see no one race from Tamriel perfectly matches any from Earth.
Of course they don't match perfectly, but it's obvious that they have been inspired by real cultures.
The Mongols conquered and built an empire too. So did the Aztecs. And the Osman Turks. And Shaka Zulu.
The greatest resemblance is how the Imperials live in peace with the other races, despite their conquering. It's like Pax Romana.
And comparing the Imperials to Romans makes me sad. It makes a little more sense (though still not that much) if you look at the Imperials in Morrowind, but most people nowadays think about Oblivion. And pretty much the only things the Empire in Oblivion has in common with Rome is that they have an emperor, a lot of provinces and that they call their armies legions.
Look at this article, second piece of text. I think it's pretty obvious, but oh well...
http://www.uesp.net/wiki/Oblivion:Imperial