One area of caution would be the workload Zambrano had last season. He was one of only three pitchers in all of baseball to average 112 pitches per start (Livan Hernandez and Jason Schmidt being the other two).
On a side note, I tend to strongly disagree when people use innings pitched to discuss pitchers' workloads. Better pitchers get more batters out, and an inning pitched is just three batters retired (better pitchers throw fewer pitches per inning). Pitch counts are much more imporant, and specifically, games in which pitchers push further and further past the 100 pitch mark, when the risk for injury increases dramatically.
Zambrano was also third in the majors in Pitcher Abuse Points
, again behind Hernandez and Schmidt.
Maybe Zambrano's big frame will allow him to endure such a monsterous workload. However, with the Cubs bullpen situation, I wouldn't look for Baker (who has a strong track record of getting a lot of use out of his starting pitchers), to ease up on Zambrano's share of the team's innings. If Zambrano is going to continue to throw 200+ innings a season, you would hope for the sake of longevity that he'd become a little more efficient.
I think if Zambrano doesn't get worn out or injured, he'll best Hudson in fantasy worth, but his past and expected workload is something to consider.