Hi. Thanks for all your replies.
The Oxbow is to mix with the food he's been eating, not to give him as a sole feed.
We picked it specifically because of the nutrition content it has and because someone we know at another rescue org recommended it as a
supplement to his feed until he's a little less pudgy. The original owner and later the people who took him in temporarily had him on dried fish (I saw the woman give him the equivalent of a teaspoon of it at one go, as he would do cute tricks for it), and she said they did that quite often. And the freeze-dried mealworms. There is a bottle here of something labeled "Herbage Show Freeze Dried Feast" but the contents do not look like what's on the label so I think it's a repurposed jar. Most of the label is in what looks like Chinese - it doesn't come up on Google. The jar contains a mix of what I think initially came in the jar plus mealworms (maybe 1/2) and mixed grains (the other half). I do see dried corn in there, which I was told by a breeder once was not good for them. (?) The main bag of food that came with him was "Vita Prima Complete Nutrition Dwarf Hamster Food." The plan is to sub some of the Oxbow in with the seeds, and portion out the mealworms so that he gets the equivalent of about a tablespoon a month of them. And the occasional small bit of fresh herbs/freeze-dried veg. Eventually we would like to get him onto a "complete" mix - it looks like I can get Higgins Vita Garden Hamster & Gerbil Food delivered to us by Amazon in a week or two - with the fresh herbs/veg remaining as treats. (Thanks for the link to the list of foods, that was very helpful.)
He came out to greet us a while ago and had some floor time. We just put his little sleeping box out with him so when he had enough "out" time he could just go back into it. Which, after a bit, he did. He seemed to be alert and enjoying himself. My daughter said she got up in the middle of the might and found him walking very slowly in the wheel, so that's good. At least he's moving around. It looks like he made several nests in the bedding of his cage, as well, overnight.
I have phoned a half-dozen vets, and the ones that take small animals (pocket pets) don't have an opening until January. The one closest to us is not taking new "pocket" animal clients at all.
I did get one that said if we had an emergency situation to phone them and they'd try to work with us, though. So that's at least a little positive. I don't guess I'll be getting him in to a Vet any time soon.
Also, the "protein funk" he had when he first got here seems to be greatly lessened. It's not his bedding, it him. And it's not that we've gotten used to it, as I was out back for a bit and then came back in and handled him. I really do wish I could get a vet to see him sooner.