Is the GameGuru Loader permitted for this jam? Also, are the assets in the DLCs for TheGameCreators products permitted? I know they are licensed for release in a final product, but I'm not sure if this jam requires source and assets to be submitted as well which by my understanding would violate the license.

The Jam only requires a final game, no source is needed, but you are free to include that if you want.  GameGuru Loader is an AppGameKIt tool, and so acceptable.  You may use any media you have the rights to, providing that you adhere to the terms of distribution. In the case of TheGameCreators DLC, you are free to use it in a free or commercial game, providing a reasonable attempt is made to protect the media.