I have three male dogs. I have had male dogs before. All of my dogs were neutered and all the dogs I have now are neutered. I have a labradoodle that was actually neutered before he was shipped to me at eight weeks old.
I have a mutt from the SPCA that was neutered very young as well and I have a 14 year old Labrador retriever that was neutered at a few months old.
All of my dogs hump. They aren't chronic humpers, but they do hump. In this case, it is definitely not testosterone driven, it is dominance.
I have found with most dogs I have had that the humping thing is merely one dog telling the other dog, hey big fella, I am the "top dog" around here, so take that! The other dog responds in kind by either a growl, a snap or a return humping!
I just yell, "break it up fellas." However, maybe you could visit: stopbarkingnow.com. Sounds like a pheromone device might help calm down the savage beast.