I stand corrected yes it does require a voucher.... if you go to the website there are three things to click on:
1. Terms and Conditions
2. Rate voucher
3. Book your reservation.
I'm tellin' ya though as long as you know you are going and wont miss the date it's gold... it'll save you a ton on travel as long as you are willing to accept that if you don't show or need to cancel you are out your money for that entire stay's value all nights if booked for more than one. You would also be out of your money for the remaining stay of a multiple night stay if you checked out early too....