Actually, not surprising in the least. I used to listen to ICP, up until their Bizaar/Bizarre albums (never considered myself a juggalo, nor painted my face like an idiot
), and they've always subtly mentioned their belief in God. And their lyrics generally trash racists and bigots (ironic considering most of their fan base).
The article mentions they revealed it a few years ago, so its not a PR stunt, at least not now anyway. I think the point that's being missed here is that they are rappers who are christian, but not christian rappers. There is a difference.