Just as a disclaimer, you'd be wise to disclose that the Arceus was generated using an AR. It's done exactly the same as the Event distribution (the IVs even differ if you generate more than one, and the nature I believe is random in those cases as well but I'm not 100% on that one), but you should point out it's not actually from an Event, but generated. The Giratina on the other hand is done using the in-game Event and no disclaimer is needed.
Reason I say this is that some hate AR use of any form. Even cloning.