From what I understand, is long as the skin pigment is dark the hearing isn't affected. That's one of the reasons the white german shepherd standard is so strict on having deep black pigment on the nose, lips, eyelids, and as much of the rest of their skin as possible (paw pads, nail beds, etc.). As far as I know, they don't have any higher incidence of deafness than dogs with colored fur.
White GSDs are not the same genetically as a white papillon either. It's not piebald but rather a really really light cream and fully pigmented. It's important to remember you can get the same physical 'look' by different genetics. There's recessive and dominant ways to get a black dog for example. Or the example that you can end up with a merle dog with a lot of white both by it being a double merle or by it being a color headed white (merle + piebald).
However, JRTs are colored genetically the same way as papillons. A white JRT is a very very extreme piebald. A white papillon is the same. It makes sense that white heads would be linked in both breeds to deafness. All papillons are either piebald or extreme piebald. White spotting essentially blocks out pigment completely in those areas, which can lead to issues. Now, a dog with white colored ears CAN be able to hear if the pigment is deep down inside the ear, but in general you want it over the ear to play it safe.
Honestly, I wonder why split faces and bald faces with white ears isn't a problem in some breeds like border collies for example. They're also white spotted so I would think that there would be that same link to deafness in them too. There are reasons certain breeds have color requirements beyond the fact that people like the way they look...
Check out around this dog's eyes. There is no pigment around the eyes. You'd see black pigment there if the dog was something like a white GSD or a bichon. The pigment on the nose appears weak to me, but it's hard to tell. Most deaf dogs I've seen still have a black nose. Some have pink spotting on it though. Nose seems to be the last place to turn pink. Think about our dogs for example... They have white spotting around their muzzles which means no pigment but they all have solid black noses.