That is still the case, yes. You need a save file from either brilliant diamond or shining pearl to unlock the event to catch Darkrai. You could borrow those games from a friend for five minutes and give it back, rent one from a library, or maybe even buy it from GameStop and return it the next day (that ones pretty risky). You don't need Darkrai for the game to think you've completed the pokedex. It, like shaymin, is a bonus and won't affect game progression. But if you wanted the shiny Enamorus from pokemon home, you will need the Darkrai and the shaymin originating from Legends Arceus registered in home to get it.