DJ Rotom is a Rotom that has possessed a stereo system in Pokémon Pokopia.
Rotom is one of the special Pokémon Ditto encounters while restoring habitats. In this story, it has taken control of a stereo system, creating the character identity DJ Rotom. The role reflects Rotom's established association with inhabiting electrical appliances.
Pokopia gives several familiar Pokémon unusual occupations or conditions. Peakychu is a Pikachu that lost its electrical ability, Mosslax is a Snorlax covered by vegetation after sleeping for a long time, and DJ Rotom is tied to music equipment. These characters help make the restoration story more character-driven than a standard Pokédex list.
The answer is the Pokémon species, not the appliance. The stereo system is the object Rotom possesses, while “DJ Rotom” is the character label used in the game. Magnemite and Porygon are also technology-associated Pokémon, but neither is the character identified as DJ Rotom.