yes i was able to do cash and points by calling reservations.

two managers on reservations line and one gold passport customer support person all told me that they had information telling the they cannot apply the diamond suite upgrade. however, looking at all their info, they state:
An "Eligible Rate" shall be defined as any hotel published room rate, including, but not limited to rates found on hyatt.com, the Hyatt Daily Rate, Volume Account Rates, AAA and Senior Citizen rates and Points + Cash awards.

so i called again and before i even had to argue this fourth person said she was told it did work so she applied it.