I heard it was "creole" for Goodtimes, but I cannot remember the source so...................Also I think I heard it was also the title of a song........... I guess this didn't totally answer your question, thats all I got.
I believe you are correct on it being a Creole or Cajun word or something loosely translated as "goodtimes". I think Bonnaroo the festival borrowed the word from Dr. John's song/album entitled "Desitively Bonnaroo."
It's a cajun term, popularized by Dr. John, meaning "The Best Stuff" or "The Good Stuff"...The organizers of Bonnaroo say they borrowed it from Dr. John's previously mentioned album...which is why he'd be such a great choice for Grand Marshall.