I am using GM Studio and wondering if i can use an non visible object that is a 5 color, its basically a hitbox. If it never displays in the game, does it matter?

doesnt matter

As long as it doesn't show up in the final game, it's ok for this jam.

I don't think anybody will check your source to see if your debug objects respected the jam theme :P

That's perfectly fine! I'm doing the same thing as you!