Here is a pair of sentences from A Midsummer Night's Dream that anyone who has ever spent a sleepless night can relate to:
"O weary night, O long and tedious night,
Abate thy hours....
And sleep, that sometimes shuts up sorrow's eye,
Steal me awhile from mine own company."
For diagramming imperative sentences, I think it is a mistake to put an understood "you" in parentheses. Parentheses are already being used for appositives.
An "x" will suffice for the understood "you".
"(You)" is commonly used by online Reed-Kellogg teachers for imperative sentences. They say, "The 'you' is understood". It's evidence to me that they are not going to go the whole way with the art -- which ultimately has to deal with the enormous amount of ellipsis in speech.
I agree with your diagram, except that I think there was another "o" in it.
I just float interjections, nouns of direct address, and absolute phrases anywhere up above the clause they are most closely related to.
"Vocatives" I know because I have studied Latin. Here across the Atlantic we call them "nouns of direct address"