Ummagumma was a slang term for having sex. And of course Rock and Roll was originally slang for having sex as well. So, if you look at it that way, the album Ummagumma could simply mean Rock and Roll.
On the Ummagumma album cover, the last reflection in the wall is the cover to A Saucerful of Secrets.
The 'Jude' listed alongside Waters is Judy Trim, Roger's first wife.