RE: The official Super Smash Bros Brawl thread.
It IS Ness. Pokémon Trainer appeared along with Lucario, Jigglypuff, and Pikachu on the other screen shot. If you compare the screenshots, you will notice that there is a distinct difference. Download both screenshots, and zoom in on both of them in an image editor, and you will notice that the icons are different.
Keep in mind that the information on the Dojo is translated from Japanese, so the wording may vary a bit from the intentions. Plus, the phrase "up until now" was used in another update on the website, but it was clearly included in the game.
Lastly, you will notice that the icons are grouped by series. All of the Pokémon icons are together (Pikachu, PT, Lucario, Jigglypuff) and on the update on the main site, all of the Kirby characters are together (Kirby, Meta-Knight, King Dedede). So it would make logical sense that the Mother / EarthBound characters are grouped together (Ness, Lucas).
Based on these facts, I think it is quite compelling that Ness is in.