Battling a Dialga won't add it to your Pokedex. Talk to the elder in Celestic to "see" Dialga.
[agelimit]competent competitors[/agelimit]
Ichida, the Zealous Blue Partizan
Pearl Battle Record: 105-26
Battle Style: 6v6 Lv100 Singles, No Hacks, Ubers or Legendaries

To gamingly entertain the crap out of you. Yes, I said 'gamingly.'