"Creators are free to use any tools or assets they have the right to use. This includes tools and assets they have created prior to the start of the jam, tools and assets that are free for anyone to use, and tools and assets they have purchased a license to use. Proper credit must be given if required by the licenses for the tools and assets."
As far as I understand you can use any asset, but you must have the permission from the creator to use that asset in your project.