This should be irrelevant as you can definitely get at least Platinum by calling US customer service and requesting to be upgraded to Platinum prior to the stay (through a so-called challenge / 'trial' offer or otherwise).

I would suggest explaining the situation, and the 80+ room nights you will be giving to Hyatt, and asking for Diamond status rather than platinum. You should have a good chance.

The GH is a huge hotel and the service is not usually personalized, especially for guests with no status. Because you are giving Hyatt a substantial amount of business you should A) Ask for Diamond status and B) Contact management at the hotel directly to ensure that you are well taken care of. Since you have the ability to give the hotel 80+ room nights, you should have some bargaining power.