Race is a synonym of variety and breed, if you want to use other words.
No, I'm talking about the system in which humans are divided into
mostly arbitrary, but
visually distinct, races according to perceived notions of genetic relation. The words Negroid, Mongoloid, Caucasoid, etc, weren't just old timey ways to skin color, but part of a system that grouped and then ranked humans.
It would be utterly bizarre for an alien species to adopt anything resembling this system and
then declare that aliens, total genetic strangers with no shared history at all, were part of the group they placed themselves into.
Let's just imagine racist humans and aliens, for ease.
Look at the mammalian portraits for a minute. Do you think that a human racist, who believes there are white people, black people, asians, native americans, and maybe is even aware of Middle Easterners, Polynesians, Austronesians, or Dravidians but doesn't know which arbitrary race to assign them to, is going to just accept that Flying Monkey, Pig Monster, Six-Eyed Ratdog, Click-Clack Eyebrow, and Blind Platypus are in the same category as white people? Simply because they look like they warmed blooded, furred, lactating, sweating mammals whether or not they actually are?
This is what I mean by racism does not make sense as applied to aliens. You would have to throw out your pseudoscience and replace it with pure aesthetics. You'd get the Racist Humans & Sexy Aliens Alliance, securing the dominance of humanity across the galaxy and also being cool with sexy aliens having the vote. They could have gone full racist and enslaved the sexy aliens, but they didn't feel right about wanting to have sex with something that was legally forbidden denied citizenship, I suppose, so they just enslaved members of the Union of Aliens That Humans Don't Find Particularly Relatable.