It depends on the context. If the greetings must be included in a written context, they must be punctuated.
"Why do we need punctuation? Are commas and colons required only to give new writers a hard time? Punctuation allows us to clarify the meaning of words when voice or "body language" cues are removed. Punctuation tells the reader how to make sense of words alone. Poorly or wrongly used punctuation contributes to awkward writing and reader confusion."http://www.gwr.arizona.edu/overcoming3.htm
For example, in written texts (with a context) you won't find the phrases "good morning" not belonging to a certain context, independent from all the rest that is written.
She said: "Good morning".
Now, in your example, the activity is not in writing; the words they see are the script for what they listen.
You will read the same rules on this site:http://www.learnenglish.de/grammar/punctuationtext.htm
with different examples, and also here:http://mrbraiman.home.att.net/page25.html
Hope this helps:)
Syl's English Corner - Learn English And Have Funhttp://www.ginnegar.0catch.com