Using hard resets during the run to manipulate the RNG on emulators that do so inaccurately is banned. Accurate emulators for RNG manipulation are currently limited to BGB with a GBC bootrom, and for Red/Blue only. RNG manipulation on emulator for Yellow and Gen 2 games is not allowed as it stands.
This ruling is up for review based on future emulator releases, but there is no guarantee that there will ever be an accurate enough emulator released for Yellow and Gen 2.
To clarify, this does not apply to any non main series games as their RNG functions differently.