Hi.
I have noticed that wild Arceus are considered legit despite the azure flute being unreleased.
However, they do say they were encountered in Tall Grass at Level 100 so they must be cheated unless certain information is lost upon transfer. I'm not an expert on how it works.
http://www.pokecheck.org/?p=detail&uid=460913
http://www.pokecheck.org/?p=detail&uid=460909
http://www.pokecheck.org/?p=detail&uid=460886
Also Pokemon at a Level below their Level of capture are given a valid level.