Honestly... I think that if it was so simple, Nintendo would have already done it... plus that most projects at ZFGC don't reach even 10% of development...
About hecking the ROMs... as far as I know, the ROM files won't give you useful information considering you're recreating it in game maker. It's not as if you could copy and paste the data inside the ROM into your game, so you'll actually have to type every single pokemon information (how many are them? 600?) - their level upgrading data, move learning data, evolving data, their behaviour on attack/defence/speed points and etc., plus all the stages data (which pokemon appear where, with what level and characteristics, which pokemon each trainer has, which pokemon each stadium leader has, their AI data)... anyway, pokemon games may seem easy to create, but actually they take you a lot of work generating that data (specially for Nintendo, who made it from scratch). [BTW, that's why I personally prefer making action games than RPG games...] Also, you wouldn't be able to just copy that all from Nintendo, because since it is a bigger game, the pokemon of the other regions would have to be stronger so that the game could be fun enough. So anyway, what would probably happen is that after some months of development everyone working on the project would get tired of it and will have only entered some 10% of all that data...
Maybe if this was a community project it would be possible, but considering that ZFGC has been losing activity recently, it's still quite difficult... anyway, good luck with your project.