Healthy Paws is definitely covering my dog's "mild" HD as soon as he became symptomatic and started developing some arthritic degeneration as he aged -- they paid for his xrays, and they are paying for his Adequan injections indefinitely to delay the progress of the degenerative changes. The critical thing for us was that he he had no symptoms at all and had great range of motion for his whole life, up until about a year ago. Several years ago, when he was younger and we started his Healthy Paws policy, we had the vet do an ortho eval with range of motion tests, gait observations, etc. (but no xrays), along with a full wellness check up within 30 days of getting the policy, and the vet noted in the patient file that hips were healthy with no signs of any problems. That notation in the file was the key to them not being pre-existing: we set up that appointment with the vet and told him we were documenting my dog's good health for his insurance policy. That was a $50 exam fee that was well spent!
Healthy Paws does have a 1-year exclusion period for hips, and they won't cover hips in dogs who first get a policy after reaching 6 years old (but will cover dogs over 6 who've had policies in place since they were younger). The exclusion period means that after you start the policy, there's a one-year period during which your dog cannot show any signs of HD. If HD manifests during that 1-year waiting period, the hips are excluded.
It's important to realize that pre-existing conditions are determined by onset of SYMPTOMS, not diagnosis. So if your dog has symptoms of HD (i.e., a limp), it's probably over and done with already. It's in the file, they'll find it, and you should expect them to be excluded. The best thing you could do if you want to have your vet change what's in the file is ask YOUR vet to send the Xrays out to a board-certified veterinary radiologist for a report interpreting them -- it will cost $100-$200 (depending on the number of images and your vet's mark-up), but there will at least be a specialist interpretation in the file that will say yea or nea in a definitive way. You don't have to take your dog for an appointment -- the vet just sends off the digital radiographs for interpretation by the expert, and they email back the report. You cannot do this yourself though; it must be arranged through your vet. Here's an example of a service that does this -- but your vet may have someone they prefer:
There's NO CHANCE your breeder's opinion will matter the insurance company. Or the opinion of a specialist who's a friend of your breeder's. A radiology report ordered by your own vet, found in the file along with the xray, would almost certainly matter though.
For others reading this in the future, put the policy in place when the dog is healthy, before problems start, and get your vet to note the dog's healthy condition in the file about the time the policy starts. If you're getting insurance, DO NOT xray the dog "just to see" until after the policy is in place, and the 1-year exclusion period has run.