"I got cousins in the military, as far as I'm concerned they died when the registered."
Dead Prez never said anything about killing their cousins- I think this represents the idea that Blacks enlisting in the military are volunteering for death at the hands of political agenda not necessarily the revolutionaries that they might come up against. This is a popular notion of Black militance particularly fostered by the Black experience in Vietnam.
As for the teachers comment- thats not in the context of the song thats just the talk at the end- he did say, "as far as Im concerned..."