Hi:
Good to see that Hyatt is taking care of its loyal customers...
I just returned from Osaka myself and also had trouble finding a room at the Hyatt. Another reason that may be causing the lack of rooms may be due to the cherry blossom season. It was nearly impossible to find a room in Kyoto either...
Ended up staying at the Ritz Carlton Osaka and was very happy with the room - big along with a spacious bathroom. Staff were very courteous and helpful. It's conveniently located about 10 minutes (walking) from the Osaka station...