Vet based his "great" comment on the work he did with the hoof-tester, not on the shoeing.
I was thinking more about the long underslung heels rather than the shoes. OK, sounds like vet just meant there wasn't any obvious sensitivity, nothing about hoof form. As for hoof growth, yes, it does change, for a number of reasons, so while 6-weekly may be a good schedule for this horse some of the year, that's not a given & you may have to get him trimmed more frequently in some seasons/situations. Generally I find 4-6 weekly is reasonable for most.
The farrier said that the angle on each individual foot are fine, but that the front feet don't have identical angles, so they don't match each other - hence the wedge on one foot to bring them into alignment with each other.
I thought perhaps the wedges were in order to attempt less pressure on heels to allow them to stand up more. Is this making matched pairs based on the whole horse, concurrent with bodyworker or such? If not, how does he know the horse doesn't innately, or due to shoulder injury, posture or some such, need his feet to be odd? Among other sources, on the hoofrehab.com site you'll find an article on 'club foot' which should help you understand this a bit better. Generally the feeling about club feet is to trim/shoe what the horse has got, rather than trying to create an aesthetic ideal.
She also reminded me that when the farrier comes out in a couple of weeks, he's going to pull the shoes off for the winter. I gather it's the practice in this barn to have the horses go barefoot in the winter
That's great. Aside from it sounding like the horses don't need shoeing over winter, it is generally accepted that it's not great to shoe a horse long term without respite. Having the winter off will allow his feet to recoup a bit from the effects and with a good farrier & regular hoof care during this time, you may be able to resolve the underrun heels by the time you want shoes on again - I find underrun heels are far easier to deal with bare.
Now that I see what happens when these guys don't get enough exercise it just makes me want to ride even more frequently.
Yeah, free movement & exercise is important for horses, for their health & soundness, as well as behaviour. Don't forget, if you're feeding high energy feed because he's been in a lot of work, cut back on this too. They can do a lot less in a snowy winter left to themselves in the paddock, so working them regularly, be it riding or otherwise, can be even more important. You might want to look into hoof boots(try Easycare for a wide selection & lots of info), if you'll be riding him on hard/rough ground & he doesn't cope bare.