Emulators from third parties not related to the original publisher are using copyrighted firmware and the only way you are going to play games realistically is using pirated images. I'm no making a moral judgement. Plenty of movies have fallen off of the back of truck onto my Plex Server.

The company that owns both the original console and the copyrighted game is free to publish a game that runs on top of an emulator. Sega has plenty of games on the App Store that are basically the emulator bundled with the game image.