Ok so in summary:

I realize that this is just one GM's response, and that he may or may not know what he is talking about. It seems contradictory that voice-activation inputs are ok but AHK duplicating keystrokes to both instances of WoW isnt. It also seems contradictory that using one keystroke to perform the actions of multiple keystrokes is illegal, yet you can do this with the in-game macro system which certainly isnt illegal. So take it for what its worth. If you have been using AHK for a while without any issues from GM's, or you've had a GM tell you something different, more power to you. Personally I will continue to use AHK in the way that I believe is safe from being a violation. I made this post because I have seen several people who are interested in dual boxing asking if there has been any statements made by blues or GMs, because they are unsure if they want to take the risk of getting banned. This is just the information I got from one GM, think whatever you want about it and make your own decision.