I think is exactly the opposite, Eminem used to ghostwrite for Proof. On 'When The Music Stops' the only one who's name doesnt appear on the credits is Proof's, and his verse is quite lame in that song. On 'Devil's Night' (the album) Proof's lyrics are quite ok, but on 'D12 World' his style went down the drain. [On Encore's 'Never Enough' it's obvious 50 Cent didn't wrote his verse

there's not even one single track on his entire discography where he uses such a high quality flow.] Eminem would be pretty offended if anyone mentions to him he doesnt write his own lyrics. It's like sayin The Beatles never wrote their own songs!
Somebody mentioned that since Proof died (R.I.P.) Em's style change radically.. well, what would happen to you if you lose your best friend, your life brother?? Proof was a huge influence on Eminem since day one but in a spiritual level, not artistcly. They loved each other and were perfect for each other (nohomo) and Em's life is not the same since that moment, well, he almost died too destroying himself. Peace.