They've never done anything special when I've been there on the 5th. I always just wish him a Happy Birthday when I'm looking at the Castle and thanking him for even making the park for all of us.
A few weeks ago, I was at the Magic Kingdom. A lady was talking to her family about the Partners statue in the hub in front of the castle. She told her son, who appeared to be about 12, that it was a statue of Walt Disney with Mickey Mouse. The kid seemed surprised. He told his mom that he didn't know that Walt Disney was a person.