I've read about this, too, and I am not 100% convinced by the mink theory - though it's probably the most feasible suggestion.
From the details the stories give, I wonder why a) Dogs jump at that particular point on the bridge each time. Minks do nest near rivers and have a strong musky scent - but why always at that point? b) Dogs seem to jump when going towards the estate, never when going away from it. If the mink smell was strongest at that point for some reason, they would surely jump when crossing the other way as well c) There is no evidence that dogs go crazy looking for minks once they reach the other end of the bridge.
There is also the fact that only dogs with long noses are said to jump; why should this be? Long noses don't necessarily signify a stronger sense of smell; beagles and bassett hounds have even better smelling power - don't they ever try to jump?
Squirrels are said to nest under the bridge itself, but would a squirrel scent or sound be strong enough to lead a dog to jump? They say many dogs have died there since the 1960s. What about pre-1960? Mink arrived in Britain from the 1930's onwards for fur farming and some escaped. If no dogs jumped before the mink came, as your hub suggests, that would obviously support the mink theory.
The stories tend to be written with a view to entertain and enhance the mystery rather than solve it, so it's hard to find all the facts. If I took a dog there, I'd keep it on a leash!