Yeah, checked again, and the mistake, of course, was mine. I was thinking there was supposed to be a hex value in a field not used until Platinum, and that Arceus is from Diamond. To sum it up: my mistake, Arceus IS completely legit. :)
It is legit. I'm sure of it. I just have to find out why the hex values are strange. I'll update you on this as soon as I discover. But don't worry. If I find out something went wrong, I'll refund you.