First off I would go get a second Opinion no vet should disregard your concerns no matter how little or minor they are.
You can go to a vet and have his hips OFA certified. This is done by the vet usually takeing your dog for a few hours, Putting them under and having the hips xrayed. This will cost about $150 to $300 You can then send them in to the Orthopedic Foundation for Animals
http://www.offa.org They have a group of Orthopedics that look over your dogs hips and rate them Excellent, Good, Fair, Poor. Doing this will give you a better Idea of how his hips are. Since he is such a big breed dog hips are very important to monitor as well as Elbows.
Good Luck And I Hope To Hear What You Find Out,
Diane