This promotion, and whether you can redeem at any specific hotel are completely separate and unrelated transactions. While the promotion trumpets a free night in their advertising - it is nothing of the sort.
During this promotion, you will get a minimum of 8,000 points for every 2 stays. You are then free to do anything you want with those 8,000 points. If there is a hotel that offers a free night for 8,000 points - you have received a free night. If that hotel requires more than 8,000 points, you will need to supplement to get a free night. Hotel redemption rates can change at any time, and this has nothing to do with the promotion.