It's probably a 3rd gen event Celebi, because I can't find any information on any Celebi released for HG/SS. Which means I'm not sure if it'll trigger the event or not. If you want, when I get to that part in the game, if you let me borrow Celebi and I can test it out.
I'm worried about an event Celebi being released during the summer, when I'll be unable to access it :/