He certainly could have. My guess is -
If the reporter had just used his name - ...joined now by R. Kelly - no article would be used.
By not putting /the/ in front of the phrase, he is making it more a part of his name (who he is).
That's an easy question for me: any non-journalistic context.
The practice of making a "title" out of someone's occupation, I'm pretty sure, was a journalistic invention, maybe a way to save "ink" in newspapers.
It saves you from saying "I'm being joined by R. Kelly. Kelly is a famous singer/songwriter."
I'm not surprised that your example is spoken by a reporter.