Nathan McCullum isn't good enough for test cricket, period. He's a bits & pieces cricketer who would look way out of his depth at test level.
Anyway, if the New Zealand selectors had any sense they wouldn't play Jeetan Patel unless Vettori got injured, or one of the pitches was suppose to be a massive turner. I think most of us agree that Patel is going to be rather ineffective during this series, we can only hope the selectors see that too. Kane Williamson didn't exactly get through a lot of overs last season in domestic cricket - I think it was about 15 overs a game on average but he's good enough to do more IMO. Yeah, he doesn't exactly keep it tight but he looks to take wickets. He gives it plenty of flight and gives the ball a decent rip, give him 15-20 overs a day and he'll do well enough.