all the data/codings of all the 386 GBA pokemon are already in the Safari Zone Pal Park in the DP. so YOU MUST insert the corresponding GBA Pokemon in your DS or it could mess the codings.
If you have Japanese insert the Japanese GBA.
Once you inserted the GBA, the 6 pokemon will trigger their respective data thus releasing them in the battlefield. Then, DP has a script that will "command" the GBA game packs to release the triggered pokemon (that's why you should be in the Pokemon Center and can shoos with the PC as it has the "release" option). this is also triggers the corresponding codings for the wild version for the DP (IE. FireRed for Magby)
That's what I heard on the secrets of the PalPark. im not sure but it convinced me, for some reason. i dont know about you. sorry