I'm sorry this poor little guy came to you in this condition
, poor thing; glad he is with YOU though. And yep, there are probably many others who have suffered at the hands of those people - so I commend you for wanting to do something about it.
I'd report them to AKC, the local Humane Ass'n., the USDA (in case they are a USDA breeder), and your local city's shelter as well.
As far as health -- yeah, I'd be concerned too. There is a ton of development that takes place during those first several months and especially weeks of a pup's life. Not much you can do about invisible potential damage at this point, other than support him w/ good nutrition and do NOT overvaccinate in any way, shape, or form.
I also do believe that when a puppy suffers at a young age from something (giardia, malnutrition, some disease, bronchitis, kennel cough, whatever....), that there is a much bigger chance of later allergies setting in (enviro allergies...ie, dust, grass, pollens etc). So if this were me, I'd personally be staying away from the more typical allergens for canines like grains and such. I'd be feeding grain free for life.
If you do want to supplement him, it can't hurt. I like Natures Farmacy supplements and they make some really nice general supps.