Fine Hotels and Resorts. It's a booking portal which is part of American Express Travel, but its own separate sub-portal which is only available to Amex Platinum and above/similar card holders.

It's one of the few 3rd party booking portals which counts as qualifying nights with Hyatt, and lets you use your status on your stay. Amex gives a $200/year credit for Amex Platinum card holders for bookings made through the portal, but there aren't many options for booking through the program that are good deals. Traditionally, Vegas has been one of those few good deals.

Fine Hotels and Resorts also has a lesser category in the portal called "The Hotel Collection". Basically hotels that typically aren't as nice as "FHR" labeled properties. Not all The Hotel Collection properties which are Hyatts will give qualifying nights, but all FHR properties do.