First, to answer your question, so that it cannot be said that I didn't do that: YES, you should have very detailed information on the grandparents, including but certainly not limited to their health histories...as well as littermates and other dogs produced within the line. Genetic issues often skip generation, or may show up only in some dogs from the same litter.
They 'have to be USDA breeders?' Then they also 'have to' obide by USDA regulations to keep that status--regulations that are not fit for dogs. Nor does it change the fact that they sold their dogs to a broker, whom you purchased him from, at a VERY early age--you say you got him a 9 1/2 weeks and at that point he'd already been bought and transported across country. And, you still don't have info on the other dogs in his line. This is your idea of a trustworthy, reputable breeder? And a dog that should be bred? (Not to mention that he's just the stud--takes more than just a stud to produce a litter.)
I'm really not concerned with if I come across as a "mean" person. (Let us not get into a comparison of what people come across as.

) I'm more concerned with coming across as a person interested in the health and well being of dogs, the overall promotion of the breed itself and one who does not condone unethical breeding practices.