I think of him as a rock drummer, really, more than a hip-hop or R&B drummer. I saw him playing with Beck, and it was ROCK.
As far as lyrics or songwriting, it's an interesting question. Until you asked, I'd assumed he probably feels he was hired as the drummer, and would be wary of pushing a songwriting contribution, at least in the early going.
I'd say his main influence will be that spark and fire people have talked about. I expect him to ignite the whole album. But Neil's not exactly an ogre, he's taken songwriting contributions from other band members before. It would have to be up to snuff, though. So the real question is, how strong a songwriter is Mr. Sherrod?