I haven't seen any of the three movies Dyer talks about, but from his selected descriptions of the three, I see that he's trying to explain how whiteness has maintained itself as being the "norm" or neutral (141). Whiteness has "secure[d] its dominance by seeming not to be anything in particular but also because... [whiteness] is often revealed as emptiness, absence, denial, or even a kind of death" (141). Using black characters helps emphasis how normal whites are because races other than whites are super distinguished.
Basically, whites are "the endless plenitude of human diversity," and can be anything and are everything without stereotypes, keeping them naturalized (145). I've never thought of whites being "death" as in Night of the Living Dead, but I see the binary contrasts that Simba shows.
This is interesting because it's always a big deal or something racist when there are races other than whites. I really don't know about recent films or shows that use whites as dominant characters, relying on blacks to show how normal they are. But I was just thinking about--and this might be on another tangent, but--the Wayans brother film White Chicks because it is the inverse of "blackface" and tries to show how white girls are (or basically any girly stereotype because this is a change in gender as well). This is quite a twist that emphasizes what blacks aren't to show what whites are, including their manners and music tastes.