UFOs and the National Security State Vol 2 by Richard Dolan covers this event briefly. There is not much to it and nothing to corroborate what happened if it indeed happened.
The story goes that President Nixon paid a surprise visit to Jackie Gleason as he was a fan. Mr Gleason expressed interest in UFOs (a long favorite subject of his) and President Nixon took him to a secret base where Mr Gleason saw alleged aliens. His one time wife told of the meeting to the National Enquirer and claimed Mr Gleason was very shaken up the next few days after viewing the bodies.
Other than the article and a few authors looking in to it, no evidence has shown up to support this story. Also, it was almost impossible for the President of the USA to sneak away from Secret Service like President Nixon allegedly did. (There are some agents who say it can and has been done though, so the story is not out of the realm of possibility.)