I see "Theme" as a rating category, but I'm unsure if that means "use of the given theme" or "invented a cool theme"

It's "use of the given theme". In game jams, theme usually refers to how well you implement the theme into your game

Then What is the theme

Well....that's to know on the day of launch

Some game jams announce the theme before the jam starts, but a lot announce it on the day of launch. We have a game jam theme and an artistic theme. The artistic theme is just the art style of the AI model (i.e. Sea Life). Once the AI model is perfected, we'll let you guys know the artistic theme in the server. I suggest you play around with PixelVibe to make sure you know how to generate your own art for when the time comes