Do you have any source on this?
Viewing post in Can I use a platformer template and build the mechanics on top?
It's a game jam at the end of the day, it's mainly about the fun you have making your game and less about your design expertise. The rules say "You are allowed to use pre-made assets!" and that type of code should definitely fall into this category. If you use external assets, be sure to provide a link to where you got it from when you upload your game, but it should be absolutely fine.