I think a big reason why there's still all sorts of pronunciations out there is because Rondo's own teammates still call him Ray-john. Pierce especially does it all the time. I think Scal and Doc occasionally do it too. Don't know about the other players and coaches, as most of them refer to him as "Rondo" during interviews.
But when Rondo says his own name in videos and such, it's definitely Rah-john.