It would seem like Huey actually wasn't the lone Southern politician who was halfway decent to black people.
E.H. Crump, among others gave patronage to black people for their votes and political support. Earl Long- and maybe even LBJ- also fall into that category. Huey is just the most inspiring one because his message sounded the most economically radical, while not being outright socialist.
At the end of the day, mapgames are half textbook simulator, half storytelling device. So a balance can be made. I'd characterize Long as a self-aggrandizing opportunist who, while not straying too far from the prejudices of a man of his time and place, was fairly mellow towards African Americans. So given historical constraints, he won't be getting rid of Jim Crow directly or pulling an LBJ. On the other hand, for the purposes of story, we can imagine him doing things that we, the modern gamer, support, thus given him more moral strength.
I think he hates the far right and the Klan just as in real life because they're a bunch of ruffians who are dangerous to law and order and the stability of his regime. He also doesn't approve of genocide. But most white Southerners in that time period were likely the same- yet they accepted segregation just the same. Which is why I suggested those two aforementioned paths that Huey could
potentially take in order to 1) enfranchise and empower black citizens and 2) break the back of the traditional (white supremacist) institutions.