It is a good argument. "Are Musicians allowed to be Religious?" Many have tried and made the argument (See: Music being banned in Muslim countries, despite the Quran issuing no such order.) Others have failed.
IMO, this sounds like playing favorites and abusing the scriptures. Creed and R&B Singers, etc., are allowed to be Christians, yet, Rappers are not. It is a double standard. One raps about crimes/sin, therefore, one must necessarily commit crimes/sin in real life and their raps must only seek to glofify such behavior---it being `impossible' to simply explain or ridicule it.
This sounds exactly like something an Atheist would do, pointing to scriptures and religion just to piss people off, purposely disregarding the larger argument and using the flawed interpretaton to separate a Christian from a rapper they believe to be Christian, by saying the one cannot be a Christian because of his job, and that the other is, damn near, putting his own Christianity in the crosshairs by continuing to support such a Non-Christian.
I'm with the other guy.