I'm nowhere near the status, but was just on the Enchantment a few weeks ago. There is no lounge actually called the "Diamond Lounge," but maybe they will designate one of the lounges (Viking Crown, for example) for members only.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)