One note relevant to this: would it be acceptable if an online game also featured bots?
Their behavior would of course be extremely basic, they would only serve the purpose of showcasing the game’s features in the absence of other players.
Without bots, even if the jam becomes modestly popular and the voting period is kept short, creators still risk falling into the usual circle with online games: Player A joins -> No one else to right -> Player A leaves -> Player B joins -> …