For what it's worth, the Munich Park did offer me breakfast at their downstairs restaurant. However I am very disappointed by this new "policy" of theirs. I've always enjoyed staying at Hiltons in Europe because they've always treated me very well as a diamond member. This last stay was a harsh reality check that I may need to rethink my loyalties.
I also called the Diamond Desk about this and they hadn't heard of this policy. They seemed very surprised by it, but said they couldn't control what Hilton International does. They said that at any US-based Hilton property (or Conrads, which they said are run by the US group) diamonds get lounge access.
Perhaps there should be a master list of Hiltons that deny lounge access.