Don't forget Sechel. When it comes to Sith and Force-Sensitivity, that was more of Bioware's line at the time, than the current situation in the lore. The point is that Non-Force Sensitive Pureblood's are stll rare and it still doesn't really fit the backstory as well as the other races.
Considering what he see on Korriban for the Sith Warrior (specifically the Assistant Overseer who directs you to your class trainer); there still seems to be a Higher Status for Pureblood's, or their traits of Purebloods are just highly desired. Also, isn't the reason for Sith lineage being more highly prized because it increases the chance of having Pureblood offspring?
Onto the original question, I like to think that the lore version of the Inquisitor is a Human. We do see many Human Slaves in the Empire after all.
I always viewed it as the actual Purebloods are haughty a-holes who believe themselves to be genetically superior to anyone,including humans and hybrids, due to their increasing rarity; but that a "Purebloods are the apex of Sith" is not a systemic attitude in the Empire. If that were the case I doubt they would have human DC members.
As for the original question, I would exclude Purebloods as they are not a slave species;and from a personal view I would exclude Humans(despite some of them being slaves, they are one of the "elite" of the Sith) and Twi'lek due to the lack of lekku on your ancestor. The other species fit well, because they are viewed as slave species by the ruling elite. My Sin and Sorc are both Chiss, because I like the Chiss and they fall into the non-elite and outsider status that fits perfectly with the overall SI rise to power.