I think on AEA contracts you are fine, since most (if not all contracts) have an out clause. As long as you are not on TWO contracts at the same time without both knowing about it your are fine.
I don't think there is a legal question in play.
The question is more of a "What type of manager" are you?
In the case of this interview, it was a 9 month tour, and the last stop I would not be able to do - in April. The show that I would need to leave for has been rescheduled several times. Friends said don't mention it all, you have an out in the contract and as long as you can honor that. My issue, the show I would depart from early is all over my resume, and several press announcements are out . . . pretty obvious I am doing it.
So, in my case, I brought it up, and they very quickly said that the early departure, with this much notice, was no issue, and a firm job offer came through. So, I feel I did the right thing. Other people have lost the job because of a conflict.
In the end, how honest do you want to seem . . .