9th isn't that out of line with where he should be going. Lemme guess... LT, ADP, Jackson, Gore, Barber, Brady, Westbrook, and Portis or Moss all went before him? The only real reaches there are Portis/Moss and MAYBE Brady (though I think you can make a case for him...) Beyond that, I like Addai about equal to Barber. I like LT, ADP, SJax, Gore, and Westbrook more than Addai this year. So I'd see 6-8 as reasonable. 9 just made him the obvious pick.
I think Chicago will have a better run blocking game in the first week or two this season than they had all of last season, so I wouldn't put much stock in how he does in week 1 (though you have every reason to be optimistic.)
The line health does diminish Addai's value a little, but it's the Colts, and they're gonna find a way to put up big offense no matter what.