App developers are responsible for the content the emulators can include (which are called mini-apps)

So let’s say I am Square Enix. I own the rights to Chrono Trigger. I can release an emulator with Chrono Trigger SNES ROM and can sell it as Chrono Trigger. I cannot have said emulator allowed to run Super Mario World, as that would get my program delisted from App Store.

This is not limited to just emulators though. We can classify the games in roblox as mini apps; so let’s say if Roblox doesn’t remove a game that clearly infringes copyright; they too will get removed from App Store. (Which is one of the many reasons why they try to remove the games that contain these content)