I doubt it. I am surprised reservations would be taken until the hotel had a firm opening date. However, assuming you do have one and you wanted to take advantage of the guarantee, you would have to try to check-in. But with the property not open, this creates a problem, doesn't it?
I would, as they have a contractual agreement to offer lodging, and since they do not have rooms, they should have to find you rooms elsewhere plus pay the promised penalty. They probably will claim 'force-majeure'. Let me know what happens and do not cancel the reservation.