I totally agree with the comments about drafting him in the 4th. His rookie season would be a developmental year anyway and the team has shown with Sean Lee and Carter they aren't afraid to redshirt a player to get a good talent a round or two later.
On top of that I still think we resign Waters at the end of camp if we don't spend a 1st round pick on OL, so I love the idea of getting Thomas in the 4th.
Lee wasn't exactly a redshirt, but yes he did have a significant injury history. Carter was one for the most part, and of course, Johnson has been. The difference is that those guys were all expected to play at least somewhat during the season. Thomas most likely wouldn't be able to play at all this year, and they'd be drafting a guy that would only be a month out of surgery. Could happen late, and he could be a good future pick, but I don't know if we can afford it. Plus, I keep reading about how McClay has a reluctance to want to draft guys with injury histories.
As for Waters, you're likely right. Either that, or a guy like Brisel/Dahl/Clabo - guys who will likely be available into the summer.