No... Warrel comes up with all the vocal melodies himself. Jeff said that one time he came up with one to go with a certain riff, and Warrel told him it sounded like shit and made a new one up.
Drums are (from what i can gather) come up with totally by Van, who records numerous different drum tracks while listening to the entire song, then he and the rest of the band chooses the one that sounds best. The solos are subjective to who wrote the song i guess... but you know, im pretty sure that the solos taken on by Steve in Final product and Psalm of lydia were written by him. In terms of Medicated nation which was written by Jim, the solo was obviously written by Jeff. I doubt that Jim can write a shred solo on bass in Jeff's badass style.