We are only creating a game map from his picture. We are not publishing or reproducing his items in any way so I don't think you need the authority. It is no different than using National Geographic maps or something like that.
I was planning to download the Topo Maps he has posted and he has some graphics and stuff added. We would only use the Topo's as reference and not really post or reproduce them, but figure it can't hurt to contact him just for the heads up.