Assuming he starts getting consistent minutes, I think Tiago's role will be different every night.
He's going to be asked to set picks and muscle in the paint and do a bunch of stuff that won't appear in box scores. Other than that, it's going to depend on matchups. On offense I see him a lot like Oberto, taking only what's given to him, (except without the range). The nice thing is that neither he nor Blair (nor Bonner) will slow down the offense if the Spurs want to run.
I do wish he was a better rebounder than he's shown so far.