Boosting is dishonest, and to some, we look down upon it. Can you be banned for it? I suppose you could.
Actually, no you cannot get banned from XBL. The XBL Policy Enforcement Team has said time and time again, they don't care if you allow your Friend to shoot you in the head X number of times. It's using nothing more then what
the Game was built with.
Some Developers on the other hand can and will Ban from their Server end. Bungie is one such Dev that does not take Boosting lightly.
You can't get banned for boosting. I boosted all the time in COD. Boosting is playing within the rules of the game. Anyone who says that you can get banned for boosting is not someone that I would take advice from.