"I know Will Mayes. He's a good nigger." (1.2)
It's important to notice that Hawkshaw doesn't say "good man." He might like Will, but he isn't innocent of racist attitudes, speech, and probably thought. This reveals that he shares racially denigrating speech with his fellows.
"You damn niggerlover." (1.15)
We should note that Hawkshaw doesn't deny the slur, or seem offended by it. Although Hawkshaw uses racist language unacceptable today, it's possibly that his ideas on race were rather progressive for his time.
"Are you going to let the black sons get away with it until one of them really does it?" (1.37)
McLendon here seems to be admitting that he knows Will is innocent. For him the fact of a rumor connecting a black man and a white woman is a death warrant. He wants to make clear to the black community that such connections won't be tolerated, not even in rumor form.