Yeah, dual-slot functionality (Pal Park) will work, provided your rom as the same region as your game cartridge. I've tested this using a spare Ruby cartridge with a Pearl rom before, and there were no problems. On that note, all English Pokémon games are considered "same region", so you could transfer Pokémon from an American GBA cart to a UK rom and vice versa.
im pretty sure migrating to platinum is possible for any non crap flashcarts. R4 regular or YSMENU works perfectly but somehow couldnt do it on r4i before though :/. ive done it on the R4 lotsof times on all gba games except emerald since i dont have the game.
You mean the original GameBoy games (Blue and Red)? Not possible, otherwise the GBA games can be transferred six in a real-time day over Pal Park.
I'm doing it daily with my Firered Game and my Platin Rom. For some strange reason I don't need the national pokedex on my firered though.