Well the third onw is indeed Arceus, the image fits very accurately, but the first one looks a bit odd for me. And I'm sure the second one is Pikachu on the right side, but on the left I don't think it's NEP. Maybe there's our new Pokémon.
Anyways, even if there's new Pokémon there, there's no reason to think it will be featured in HGSS like UL said. Just think of the Lucario movie. Going by that logic, Lucario would have been catchable in FRLG and in Emerald, but gues what? That was not the case. So if we get a brand new Pokémon (Dex number post 493), it will be a preview ala Donphan and Lugia in Gen I movies and not a true gameplay element for HGSS.
Well, crap. Here I was gonna make some theories and stuff. The first is obvious Arceus, and the third now looks like it is, too. I actually thought the third looked like raichu ears, too. But it isn't, I'm sure now.
The second is pikachu in the top right jumping and the bottom left is notched ear running (pikachu is obvious, pichu's ear and foot are visible in the bottom left). It's a common pose for those two. It's entirely possible that the reason they didn't show the pictures for these is because they're supposed to be secret parts of the collection. Like when they make figures and have some silhouetted ones with question marks in them as the secret and rarest collectibles. Or they could just be some more forms of arceus they haven't announced yet. Like the different elemental forms or something.