That’s a great question. I don’t have an opinion about that specific phenomenon. If I could think out loud, I’d say that their speech might do both of the things that you mention. Because they do both, and probably in equal amounts, it’s likely a net neutral.
However, as I say, it depends heavily on how the message is crafted. Kanye West’s infamous “George Bush doesn’t care about black people” sound bite after Hurricane Katrina was an example. It was likely just as motivating to people who already saw Republicans as not caring about black folks as it was to Republicans who disagreed with that characterization. Had it been more seriously and thoughtfully presented, it may have been more a net positive for him and his cause.