Ever since my kids started school, we have only been able to go to disney during their spring break. Here that is always the 3rd week in April. Sometimes that is the same as easter, it was in 2006. We always have been able to use a AAA discount for our room. I do try to call and get it added to my reservation as soon as they come out, but it has always been offered. I am not aware of any true blackout dates for the AAA room discount. The only issue is whether there are any available for the resort you want and the dates you want.
Christmas Week - thru New Years Eve. This year, I think it's starting December 18.
Otherwise, the AAA discount is available on a first come, first serve basis. Disney never says exactly how many rooms at each resort are allocated the discount, just like when they release their own promos (AP rates, Florida res rates, package deals like free dining or upgraded tickets).