I haven't looked into that case but for some MCUs you aren't going to notice a difference and having a dump is more of a being able to fix a pcb with dead MCU thing. The most extreme example I can think of is one of the Capcom shooting games just having a tiny check on bootup to see if it's there. The simulation in mame simply tells the game to skip it. So having that chip dumped does nothing for a gamer whatsoever. Likewise if anything more complicated is faked well enough, it'll be the same situation.