Thanks for asking - yes, it states "highly advised" and not "mandatory". I totally understand your point, but on the other hand it's a jam which will have its own given theme, and a bunch of prizes, so adding your RPG right when the jam starts and not even matching the theme would be considered a spam and the game will be removed immediately.
Maybe during those 13 days, you could create a small hyper casual (demo-like if needed) creation from scratch (incorporating the theme) that would invite folks to try the "full" RPG? It would make more sense in a way that it could end up higher in the rankings and actually get a lot more attention and traffic to your big project than just throwing it in on the list and calling it done, ultimately ending at the bottom of the rankings.