Requirement to unlock National Dex in Diamond, Pearl revealed
Recently, it became known that transferring GBA Pokémon to Diamond and Pearl entails the possession of the National Dex as a primary condition. Although the concept of the Pal Park has come to be seen as a hassle by many, the condition to making use of the facility has been considered tantamount to defeating the Elite Four, since the upgrade to the National Dex is merely a chain event in FireRed, LeafGreen and Emerald.
The latest CoroCoro magazine reiterated the information and further complicated matters, revealing that the National Dex is obtained after completing the Shin'ō Dex.
Professor Nanakamado would appear not to be as concerned with the player's feats as Professors Oak or Birch, both of whom decide to entitle the player with the National Dex at the sight of championing the Elite Four. Nanakamado apparently wants to see the Shin'ō Dex completed for purposes pertaining to his research on evolution, and only when his wish is fulfilled does he return a favor to the player (In contrast, Birch delivers one of the Johto starters for completion of the Hoenn Dex, by which time the National Dex has already been obtained.).