The hill people have come down, at the Chandler's request, to help with the cotton harvest. They are portrayed in many ways as the opposite of the mexicans who are reliable and hard-working. A conflict is already brewing over all kinds of things as the hill people are constantly shirking, particularly their ring leader who eventually murders and Luke is the only witness but feels he has to keep his mouth shut.
Eventually there is a resolution of sorts when Hank is killed after attacking some of the Mexicans. Personally I think the story works itself out in a way, and the fact that Luke has to keep the secret creates an interesting internal conflict for him and teaches him a great deal.