I don't think it is a problem at all. My DF and I celebrated our 2 year anniversary of our first date in April/May 06, after him having proposed to me at DLP in December 2004.
When I called to make my ADRs I mentioned to the CM that the meal I was booking at the California Grill was a surprise (so if anyone were to call me back/contact me, they wouldn't mention it to my DF). She asked what we were celebrating and I told her. A number of CMs at check in podiums expressed their happiness at our anniversary, and at the CG our fabulous server brought us an anniversary desert.
Also, when we checked in at POFQ I had ordered DF a gift basket and the CM thought it was sweet when she handed it over. When we got back to our room after driving to Walmart for supplies she left a message on the phone wishing us a "Happy Anniversary," and the following day we came back to a card and photo signed by Mickey and Minnie, and a balloon, which this wonderful CM must have organised for us.
To counter the people who say "announcing" things means you must be loud and insecure, I couldn't disagree more. DF and I believe in karma - we try to treat everyone well and do good things, and I think it is this attitude that leads people to, in turn, do nice things for us.
Getting off my soap box now - have a great trip and a wonderful anniversary