I suppose I was thinking more about politically ruling rather than stormtroopers going out and shooting a bunch of jawas. I'm not saying that non-humans will be left in peace while the Empire goes after humans; I'm just saying that on the political level of Star Wars and Empire to a large degree, the Empire is really only staffed with humans while blowing planets up inhabited by humans while trying to crush a rebellion manned by humans.

Granted, this is a logical fallicy, using a lack of evidence as evidence, but I think that this is the best we have.