I would think that if he had hip dysplasia the shelter would have known this since he did have medical care and they are a respected shelter (North Shore Animal League).
They should have given you some sort of record of what vet care he had at the shelter so that you would have some history to give to your vet. If they did check for hip dysplasia they would have that on record. I'd suggest you ask them if you didn't get anything like this.
It's very unlikely, though, that they did check for hip dysplasia. Most shelter check-ups only check for most obvious illnesses and injuries - broken bones, respiratory infections, etc. - they don't have time or resources to diagnose or care for non-life-threatening illnesses. The dew claw, for example, is annoying but there is no
need for it to be removed; that's why the shelter didn't worry about it. He probably only has one because the other got torn off sometime in his previous life. Hip dysplasia is usually diagnosed via an xray - and the dog has to be sedated - and shelters don't have the resources to do this kind of procedure for a non-life-threatening illness.
Sounds like your dog's had a difficult life, though. He sure is lucky to have found you! Congrats, and good luck!