Fpse does supposedly support gameshark codes. Its supposed to support codes beginning with 80, 30, and D0. They're very temperamental however, in that sometimes they work, and sometimes they dont. The codes also have a tendency to wipe themselves from the text box. When you input it, dont use the Xperia Play's back button to back out of the menus, use the circle button, it helps a bit. And I've found that making sure the codes you use and the game version you have match up. (north american codes for north american game etc) As I was playing a PAL version of Digimon World, and the codes didnt work, then I got an NTSC copy, and the codes worked fine as they were North American. Hope that helped you a little, i'm afraid I couldn't offer any advice on the actual game, but just the emulator and the cheat system.
Jake.