To answer "yes," I don't think it's enough to have politically sounding song lyrics, or to sing at a political rally. The issue is the use of the "concert stage." To me, that means talking politics from the stage, in the direct voice of the performer. For example, here is evidence that Springsteen, in his own (non-singing) voice, discusses politics on the stage:
Springsteen was remarkably blunt in his criticism of the Bush's administration's policies on torture and wiretapping. "These aren't just things that are un-American, they're anti-American," he said, introducing the upbeat new song, "Living in the Future." "We plan to do something about it right now. We plan to sing about it. It's a start."