pumpkin is great for dogs
Pumpkin is absolutely fine to feed your dog. Just make sure it is the pure pumpkin and not the pumpkin pie mix. I fed a dog I used to have with lots of health issues pumpkin every day for about 3 or 4 years. She loved it. I mixed it in with her food mostly. Looked really disgusting, but she was happy. Sometimes I would give her a couple spoonfuls. I also sometimes mixed a little with a bit of yogurt. I have a book at home that recommends it. The book is called Dogs, Diet, and Disease by Caroline Levin. It's about Cushings, Diabetes, Pancreantitis, and others. The pumpkin is very highly recommended, because it can help with diarrhea, constipation, pancreatic issues, etc.
My dog (not the same one as above) recently went through a round of humaworm. Several days after she was done, she was biting and scratching like crazy. It took me over a week to piece it together. I had kept trying to figure out if she was eating differently, had fleas (no), etc. I even took off her collar while she was in the house, because the noise it made when she scratched drove me crazy. RG from Humaworm told me to wait a little bit and give her another round of the treatment. It was die-off causing the itching. She is still scratching a little now, but it's nothing like before. She didn't lose any hair, though.
Has your dog ever had his thyroid levels checked? My past dog had lumps, scabs, loss of hair, etc. The vet would give her cortisone shots ---- it was many years ago and before I was smart enough to realize that I need to do my own research rather than blindly let a vet do treatments like that. Anyhow, the spots would go away temporarily. They got so bad from the scabbing and peeling, that she would cringe when I touched her. I took her to another vet for a 2nd opinion, and she was then put on antihistamines (another bad idea). The spots for the most part cleared up. Then eventually some bloodwork showed that she had hypothyroidism. Once she got on the thyroid medication (later changed her from the medication to bovine thyroid extract), the skin issues completely cleared. It had been the thyroid all along. It's just a thought.
It doesn't sound like the humaworm is the cause for your dog's skin problems, though, since he had them before starting. My friend's dog had some skin issues in the spring and summer. She said the hair was falling out in one area, and their were bumps that kind of looked like big, infected hairs. The vet never could figure it out, but I had her use grapefruit seed extract and coconut oil on it. It then cleared up. That makes me think it could be a bacterial or fungal issue. If you have any grapefruit seed extract (dilluted) or coconut oil, try rubbing those on the area.