I went ahead and e-mailed Marriott about the restrictions. Here is there resonse...
Thank you for contacting Marriott. We appreciate the opportunity to provide you with information.
You can review all the terms and conditions regarding Bonus Bucks below:
1. Reservations for Bonus Bucks redemption should be made in advance by calling 1-800-899-7235 or in the U.K. 0800 221222. Customers cannot use a Bonus Buck on a stay booked on Marriott.com or any other website. They must call Marriott directly.
2. A two night paid stay is required. One Bonus Buck coupon is applicable per two night stay. (It is possible for a customer to use more than one Bonus Buck coupon per stay if their stay is 4 or more nights. For example, if a customer is staying 4 nights, they can use 2 Bonus Bucks, 6 nights 3 Bonus Bucks, etc. The customer may use a Bonus Buck coupon for every two night element of a stay at a publicly booked room rate.)
3. Present coupon at check-in. Bonus Bucks may be applied to accommodations, dining, spa services and/or gift shop purchases that are charged to the room.
4. Credit must be established at check in by presenting a valid form of payment as well as surrendering the Bonus Buck coupon.
5. Bonus Bucks coupon may not be acceptable at concessions within the hotel not owned or operated by Marriott. Please confirm with the hotel prior to making the purchase.
6. Bonus bucks certificates are not redeemable for cash or Marriott gift certificates. Change nor a credit will not be given on any unused portion of the Bonus Bucks. Bonus bucks are void and will not be honored if sold for cash or other consideration.
7. Bonus bucks coupons may be used for all publicly, listed and available room rates and packages, excluding catering, group, and contract rates. Bonus bucks cannot be used in conjunction with any other discount or certificate for accommodations.
8. Bonus bucks are not replaceable if lost, stolen, destroyed or expired.
9. Bonus bucks are transferable when gifted.
10. Any tax liability, including disclosure, connected with receipt or use of this certificate is the recipient's responsibility.
11. Bonus Buck coupons are valid for 6-8 months from the date of issue. The actual expiration date is listed on the front of the Bonus Buck certificate.
12. Bonus Bucks can be used on an advance purchase rate stay, but cannot be used to prepay the advance purchase rate.
If we can be of further assistance, we invite you to reply to this email.
Thank you for choosing Marriott.