Jango Fett...

Bounty hunter, and one of the best. His reputation had spread far and wide, so much so that he was sought out by Count Dooku and choosen to be the template clone for what would, a decade later, become the Grand Army of the Republic.
In many respects, Jango Fett, in that instant, literally became the face of the Empire.

But what if Jango Fett hadn't been a human?

We accept the Original Trilogy fact that the Empire grew to be anti-alien and pro-human, and there is both a logical reason for that in terms of story and in real life.

On Earth, circa 1976, when filming Star Wars, Lucas knew he didn't have either the cash or the make up technology to accurately portray an Empire of aliens, and so the New Order became, largely, a humans only club.
In the Star Wars Universe, the seat of power was located on Coruscant, and in the Star Wars Galaxy, humans originated from Coruscant. Therefore, there's a certain logic to humans ruling the roost, quite apart from the fact the Palpatine was human himself.

So, how different would things have been if Jango had been an alien. If Lucas had been free of financial and practical constraints, would the army of the Empire be different? Would it even matter if Jango had been an alien?
After all, hidden beneath the drone-like mask of a Stormtrooper, it would make little difference.
Or would it?
There was an ideaology to what Palpatine was aiming to achieve with his new Empire. He was more than prepared, with Darth Vader as his iron fist, to crush the galaxy beneath his heel in order to make it comply. And, while humans may well have been the most prolific race in the galaxy they would still be hugely outnumbered by every other race combined.
But by taking all the actions he did in the prequels - merging the Commerce Guild, the Corporate Alliance, the Separatist Movement, the Trade Federation - into the larger mass of what soon became the Empire, many of the massive corporations run by aliens became obsolete. Notice in the prequels that these organisations are all run by aliens, with the exception of the Separatist movement which was run by Dooku, Palpatine's pawn.
By the time of A New Hope, the galaxy has been subjected to two decades of Imperial expansion, an age of tyranny for human and alien alike. Buit would this all have run so smoothly if Jango hadn't been a human? If he hadn't understood what he was being asked to give of himself all those years before? His attitude was part of what made him so unique, and that bled down through the cloning process to literally millions of clones.
Would the same results have been achieved in a non-human subject?
Let's assume they would. Why wouldn't they? All inhabit the galaxy, all have views on the way things should be run, and many of these corporations who were turned on by Palpatine were willing participants in order to get rich and powerful.
Would Palpatine have been willing to trust his entire galaxy to aliens? Would he trust his masterplan to a clone of an alien?
Would he have trusted Order 66 to aliens?
His aides were largely alien in the Prequels, but by the time of the Original Trilogy that appears to have changed. Was he simply using them to get what he needed before jettisoning them away, or did he truly trust them?

Is Palpatine nothing more than a racist?