The structure for the Pokedex is different in Emerald. Jambo51 has said in the past that it most likely would take a lot more than offsets.
Porting things is tough. A lot of times, you can just search for the same bytes at that offset in the other rom in a hex editor. Other times, you need to find a good starting point, like a table that you know in both roms, and work backwards through pointers. There is no set way to do this. You have to be creative.