Quoted By:
Ethan: Typhlosion, Sudowoodo, Togekiss, Shuckle, Gyarados, Extremespeed Dragonite.
Lyra: Marril, Meganium, Ampharos, Quagsire, Magcargo, Noctowl. Ampharos, Quagsire and Magcargo were Primo's egg, Marril was the pokemon Lyra had if she wasn't picked, and Meganium is the remaining starter that was gone by the end of the saga.
Brendan: Blaziken, Wobbufett, Metagross, Castform, Kecleon, Pelliper. All of them except Pelliper and Blaziken are canon. The reason I put Pelliper in there, is because it's pre-evolution Wingull had importance in the game as Peeko, Mr. Briney's pet Wingull.
May: Swampert, Magcargo, Ludicolo, Tropius, Chimecho, Electrode. The first ffour are from her as a rival, Chimecho is the rarest pokemon from Mt. Pyre, the nearest dungeon to Lilycove. And Electrode was an encounter in New Mauville.
Lucas: Empoleon, Porygon-Z, Lucario, Blissey, Togekiss, Drifblim. Out of these, only Blissey isn't canon in Platinum, it is out of the egg from DP.
Dawn: Infernape, Clefable, Alakazam, Bibarel, Cherrim, Gastrodon. The first three were from her as the other PC, she caught Bidoof in the toturial, Gastrodon and Shellos's forms were important to understand Mt. coronet, and Cherrim is another explanation to Formes.
Hilbert: Serperior, Volcarona, Zekrom, Musharna, Simipour, Zoroark.
Hilda: Samurott, Darmanitan, Reshiram, Simisear, Amoonguss, Cinccino. Cinccino had imoprtance as its prevo Minccino was BW Mascot poke.
Kyouhei: Emboar, Cinccino, Mandibuzz, Amoonguss, Crustle, Male Jellicent. All are canon.
Mei: Serperior, Liepard, Braviary, Zoroark, Female Jellicent, Shiny Haxorus. Once again, all canon.