In the FAQ it says that using pre-existing assets is fine, but would it be a violation to make the art for a game ahead of time with the specific intent of using it in this jam if no actual code work is done before the starting time? Or would I have to start over?

...does this question make sense? I'm bad at communicating my ideas through words.

Hmm, maybe the FAQ isn't worded very well here. So basically that's referring to existing assets you didn't make, like ones from opengameart, etc, hence the note on crediting sources. So, I'd say it's at least not in the spirit of things to make all your own art ahead of time. You can obviously try things out to see what works, if needed. But keep in mind that most people will be doing all their work within the jam period.

Nods in understanding

Gotcha. I have a second idea that I can use instead since I kind of already started making animations for Whorse, which was gonna be a furry life/gloryhole sim.

The second idea works better for the optional theme thing anyway.