I disagree completely, I think He understands the grace of God better that any preacher I've heard. What do you think he preaches that is contrary to the grace of Christ? And did you see the line up of preachers in the front row when Prince was here in the states? Notable preachers that can smell a fraud a mile away. They wouldn't support him, if they weren't like minded about the message.
He is not directed by Satan just because He believes, even though you don't, that God grace is greater than the law.
You and I don't agree on the issue of works vs grace, but we don't label each other because of it. Prince is bringing hordes to the foot of the cross. I can't imagine God not being pleased with someone who preaches Christ's love.