This is somewhat reminiscent of 2010 again with AN being very quiet on API usage, aside from a generic post in Guru (along the lines of Gaile's reply in this thread). Not so fond memories of the result
I admit I like some of the features that GWTB gives - reminds me of the functions I was working on when I received the Dhumming (extracting player and storage item information so that I could find items over multiple characters/accounts). Given that the player base significantly smaller now, I would be surprised if they took banning action for this - however, this is AN after all so you can never be confident that this will indeed be the case.
All I can say is be careful, maybe take a historical heads up therefore and disable using the tool until such a time as this is properly clarified or a compliant version is sanctioned into the game client - believe me, there is nothing worse than losing an account caught up in something like this (especially when the tool is not being used for nefarious reasons!).