i can't speak for the people who are hosting the jam but all the textures are free and licensed under cc0 which means that you could even legally make a game and release it to something like steam, so i see no problem with it. good luck :)
" You must make all assets and code yourself or by your team within the time frame of this jam. Any templates, plug-ins and/or pre-builds will not count in the originality department. This jam is intended to practice your critical thinking, creative and coding skills, not copy and paste. Any of these will apply to the Originality category. Music must be royalty / copyright free and properly credited. so its fine to use music and fonts"
