Hally's relationship with Sam and Willie is relatively friendly by the standards of apartheid South Africa given that Hally is white and that Sam and Willie are black. But the dynamics of power are never very far beneath the surface, however ostensibly friendly things may appear to be.
Hally's spending time with these two black men is a way of getting back at his racist father, from whom he's become estranged. He doesn't value their presence in and of itself, therefore, but simply as a means to an end. Like most young men his age Hally also has a subversive streak, and in writing a school project about native dance styles sees a way of defying authority. Once again, Hally's simply exploiting an important element of indigenous culture for his own individual needs, in much the same way as his relationship with Sam and Willie, no matter how ostensibly cordial, is similarly based on exploitation.