It looks like you can install these on any hard surface even granite - I’m wondering if I install these on the DG in the backyard which is basically a hard but level decomposed granite or dirt .

Our Outdoor Sports Tiles could be installed over granite or dirt in fact we have had many customers successfully install this way. That being said, for best results, we always recommend a hard flat surface such as concrete or asphalt. This is because if it rains or floods the dirt could start to sink or shift which will make the tiles above them move.