in the video giratina vs dialga, dialga is raised to level fifty and i don't know if local battling does that.
That Dialga was level 50 all along. It was a local battle between a Dialga imported from Diamond to Platinum and an Origin Forme Giratina; both Pokémon had been trained from level 47 to level 50.
It is ironic that Game Freak had the foresight to program Rotom, Giratina and Shaymin's data in Diamond and Pearl's .pkm file with a special value that allows for distinction between multiple forms. The hackers have only now found this out; had they done this sooner, we could have anticipated which Pokémon would get new forms long before Platinum's announcement. For the record, the data for sprites, base stats, abilities and types is indeed absent from Diamond and Pearl's coding.
Clearly, Game Freak's original plan was to allow trading and battling with Diamond and Pearl; an alternate form traded to Diamond and Pearl would have been treated like a regular form, but upon being traded back to Platinum, it would have been in its new form (without having to manually switch it). It was supposed to be similar to the Deoxys scenario in the GBA games, with the exception that an alternate form used in a Diamond/Pearl game against a Platinum player would have appeared as it should to the Platinum player, but not to the player who actually used it. That would have been rather abnormal.
It is also highly likely that they only decided at a later stage that the use of Origin Forme would be dependent on the Platinum Orb, as would the use of Rotom's forms be on the overworld appliances. They obviously did not want to have the Platinum Orb accessible in Diamond/Pearl games (it would have been read as question marks and had no use); they also seemed to want to restrict the number of the same Rotom form to one per a game. Consequently, they made trading all new alternate forms impossible, even between two Platinum games. Since Union Room and Wi-Fi Club don't make distinctions between trades and battles or between Platinum players and Diamond/Pearl players - at least when communication is first created - that decision has taken its toll on Wi-Fi battles, as well.
Still, the thought of their having planned this since Diamond and Pearl only to end up setting limitations on Platinum has a certain irony to it. There was no trace of Deoxys' multiple forms in Ruby and Sapphire, and yet that did not prevent FireRed, LeafGreen and Emerald players from being able to battle Ruby/Sapphire players with Deoxys in one of its other forms.