Can I make a game for another game jam, and submit the OST for this jam?
No, the OST needs to be for an imaginary game and needs to follow the theme. However, after the jam ends you can use your OST however you like, including for another game jam.
So to sum it up: the OST must be made before the game is made.
Update: You can submit the OST for this jam if the game is not yet finished and published, but make sure it fits the theme. Cheers.
