I would definatly have the vet run a full thyroid panel. Hair loss and skin issues are pretty typical of a thyroid issue.
I am not surprised his hair didn't grow back after the vet shaved him; An unhealthy dog will not grow hair back after it's been clipped off. If you manage to cure the problem, it will probably grow back, but likely different texture.
With the yellow/orange dandruff, I'd think possibly yeast infection. It would be yellow/orange, moist, and very smelly. I'd get a high quality antiseptic shampoo, and after washing him apply cream for yeast infection on the orange spots (yes, the same stuff we women use!). Of course this is just a band-aid; I'd say there is an underlying health problem (like thyroid). Until you get that fixed, the problem will just continue to re-appear. First of all make sure his food does not contain any yeast of any sort (brewers yeast is common). They also put this in herbal flea preventatives, vitamin supplments, etc. Make sure he doesn't do any swimming, and if he's batehd make sure he's quickly blowdried; If moisture stays under the coat, yeast will thrive.
Are there any patches of black wrinkled skin? Looks like elephant skin? If so, or if there's alot of grease, I'd recommend a high quality tar shampoo (TAR only -- don't get the tar/sulfur mixtures, the two are for very different things and don't work well when mixed together).
Try running some allergy tests, and get him on a food with limited ingredients. Avoid chicken (includes anything listed as "poultry"), beef, by-products, corn, wheat, or yeast. Grains are usually best avoided but rice doesn't usually cause allergic reactions. Try out something like Duck and Potato, or Venison and Peas, etc. Just make sure to read the ingredients well and avoid multiple whole ingredients.
Hopefully you can get this sorted out! I know how much of a pain skin problems can be.
