You are forgetting Ghouls. Their former skin color is no longer relevant as they have become classed as their own, and normal humans hate them all the same, for the most part. What they did was throw the racism to another group that no one can identify with, that way it doesn't seem as bad. It is actually a brilliant psychological trick. Take away any relation with something and it no longer seems like as big a deal.
But Ghouls aren't exactly a race per-se.
Definition of race:
"Race refers to the classification of humans into populations or groups based on various factors such as culture, language, social practice or heritable characteristics."
People don't turn into Ghouls because they have the same culture, language, social practice or heritable characteristics, they become Ghouls as a result of a degenerative disease caused by exposure to radiation. What happens to them is indeed
discrimination, but not
racial-discrimination, and thus it cannot be called
racism. Ghouls may have
formed a culture of their own over the years, and may have developed their own customs due to their similar condition, but those customs weren't inherently there to begin with.
However, there is a flip-side to this argument. Another part of the definition of race is:
"As a biological term, race describes genetically divergent populations of humans that can be marked by common phenotypic and genotypic traits."
We know that not
everyone becomes a Ghoul after radiation, some may simply die. The ones who live, and turn into Ghouls must have some common factor in their DNA to allow them to be like this. There must be
something in common between all Ghouls, and it must be biological. (Possibly genetic, but we don't have enough info. to know for sure). So it may very well be considered a race.
A continuation of the definition states that:
"...This sense of race is often used in forensic anthropology anolyzing skeletal remains, biomedical research, and race-based medicine."
This both helps your argument, and mine. We know that Dr. Barrows in Underworld is working on a medicine to cure Ghouls of their disease, which could qualify them as a separate race as that medicine has been tailored for them, but then again, we don't say all cancer patients are from the same race, do we? Furthermore, Stimpacks, and other Chems, which are drugs, and in a sense, medicines, work on Ghouls (although we know Jet doesn't work to the same degree as humans) meaning human races and Ghouls are of the same biological structure. (Which we already know, anyway). Their resistance to Jet is also conceivable to be because their senses are somewhat hampered by their condition.