Well, in the terms and conditions of these gift checks, it is explicit: they are not intended for prepaid rates. So what are we arguing about here? There are always loopholes, but the potential cost/benefit ratio of making them the focus of discussion would not warrant bringing anything to Hyatt's attention!

here's an extract:
"Check Certificates Terms & Conditions

The Hyatt Check Certificate may only be accepted in increments equivalent to or in excess of the face value toward eligible purchases equivalent to, or in excess of the face value at participating Hyatt Hotels and Resorts. Multiple Hyatt Check Certificates will be accepted individually only in such increments in excess of their face value. Locations are subject to change without notice and acceptance varies by property. Not valid for Casino charges, deposit or payment for group/meeting/catering functions, or for advance purchased packages or at concessions within the hotel not owned or operated by Hyatt. In the United States and Puerto Rico the total charged will be reduced by the face value of the Hyatt Check Certificate