Yes, you can always purchase the check certificate directly from hyatt.com, but you get extra miles when you purchase from giftcertificates.com when you go through one of the airline shopping portals.

If you purchase the hyatt check certificate directly, you get charged a $2.95 shipping fee. However, you can first purchase a supercertificate (.95 fee), and then use that get a hyatt cert with no additional fee. Obviously this is worthwhile only if you order >$100 (assuming 2 miles/$). Giftcertificates.com also runs free $10 promos (with $100 purchase) at times (which is why I looked into what merchants they offered to begin with). The maximum for any one order is $10,000.

The check certificates are great for overseas properties that list their rates in dollars. They are obligated to accept the check certificates for the room price, and it saves you the credit card foreign exchange fee.

Of course, if FFN returns, it will be better to pay the room rate with a Mastercard, especially since Hyatt might stick to the T&C that states that all of the room rate has to paid for with a MC.

Giftcertificates.com also sells Marriott check certificates (but not Starwood or Hilton).