The B/Cs do seem different and unique in that regard--their stance generally is not the upright dog stance.... I've not heard of them having hip displasia, but that doesn't mean that it doesn't occur in the breed.
I recall listening to my friend's vet when her female B/C jumped out of a horse trailer on the freeway [Susie was gone a few days but we found her]...when B/Cs fall out of trucks, get hit by larger animals [cows, sheep], they tend to suffer less leg injuries and injuries in general because they roll; they are used to constant awareness of surroundings and working their bodies to the max.
That was from one of the largest vet clinics, if not the largest, in Montana.
Here, Doc Cope, while not saying the exact same thing, indicated that B/Cs tend to suffer less injuries from falling out of trucks. I happened to be in his clinic one day while he was operating on the left rear leg of a large dog--looked like maybe a cross between a Great Dane and a Boxer. All Border Collies appear "cowhocked" to me, but I'm not sure what the standard is for conformation. I've never known of one to have hip proplems...until they get kicked by a cow or run over by a pickup.