There's no internet involved, so yes it does still work, but you have to already have the legendaries / mythicals in a Gen 3 game if you want to transfer them via Pal Park.
Pal Park allows the player to permanently transfer Pokémon from a Generation III core series game to a Generation IV core series game. Once a Pokémon is migrated to a Generation IV game, it can never return to a Generation III game.
First, Pokémon must be migrated from the Generation III game. If a Generation III Game Pak is inserted in the GBA slot of the same Nintendo DS or Nintendo DS Lite system as the Generation IV game and the player has visited Pal Park, an option will appear on the main menu labelled "Migrate from ". When selecting this option, the player is presenting with a stripped-down view of the Generation III game's PC on the Nintendo DS's touch screen (the player cannot view the Pokémon's statuses, other than their minisprite, species, nickname, level, markings, and held item). Pokémon that know a move that is an HM in the origin game (called "hidden moves" by the game) cannot be migrated. After selecting exactly 6 Pokémon, the game will confirm with the player that they want to send those 6 Pokémon. If the player has any migrated Pokémon that have not yet been caught, no additional Pokémon can be migrated.