I have been told different things about getting reservation discounts from in different CMs. In January, one CM was willing/able to book a Magic Key discounted hotel reservation for me even before I purchased the pass, but indicated I would need to activate it before I presented for check in (so I could have gone into the park to activate it, then check in). I didn't end up booking.
More recently, a different CM quoted me a price on the current Magic Key hotel discount (suprisingly, it was not any cheaper than the current Visa cardholder discount), but they would not book it without me already having a Magic Key. I didn't end up following up on it because it wouldn't save me an money. I'm unclear if the Magic Key would need to be active or not to book (I don't think so...)