I just finished a two night (paid) stay at Park Hyatt Vienna. Overall the stay was very nice. The property and room was very beautiful IMHO. The service was also good, especially at the restaurand, The Bank. I had both breakfast and dinner at The Bank. Food was also good to very good.
Since I'm not holding a gold passport diamond level status I cannot comment on diamond recognition. However I received a plate of fruit and two bottles of water when I arrived. The wi-fi was also free. I tried the wi-fi a couple of times and it worked fine (and quick) for me.
I also used the fitness center. It was equipped with several machines and some free weights. The gym is next to the spa and a swimming pool. I dind't try the spa or pool thought.
Room
Bathroom