With the caveat that some emulators need BIOS files or decryption keys pulled from the original system, and you can't redistribute those even if you only intend to run free homebrew games.
And the last time that was tested with Connectix and Sony, Connectix won in the end but faced so many legal fees they still had to end up selling it to Sony and abandoning it.
Sure, and companies could also sue you for libel when you leave a negative product review. Life is unfair, but when talking strictly about what's legal or not, homebrew roms using an emulator that has a clean room implementations of BIOS should be perfectly acceptable for the App store legal-wise.
Why can't you redistribute those? You cannot copyright a key. If I bought a console and somehow manage to extract the keys, what exactly prevents me from distributing them?
If you're in the US, or the place you're trying to distribute to is under US jurisdiction, the DMCA is what forbids you from distributing DRM decryption keys. That's why emulators for modern systems usually don't include the keys, and make the user provide their own copy of them.
Unfortunately if you want to publish on the App Store or the Play Store then you have to play by the US rules, regardless of where you are, since Apple and Google operate out of the US.