Wow, Jason! Everything you described sounds very familar. I spoke with my vet today and they are going to do a punch biopsy tomorrow morning. Xrays were suggested, but the Dr. wants to have another look at it in the morning before they are deemed necessary. We've tried all kinds of things, too. We started with three weeks of antibiotics, an anti-imflammatory, foot soaks with epsom salts and daily cleanings. That stuff helped out a good bit but the problem hasn't gone away. We changed his food as soon as we got him - he was eating Alpo (poor dude!). That, and getting him off the patio he was confined to, helped out a ton! He's got some callouses on his elbows and tummy, but the skin and feet conditions improved dramatically!
We definitely should talk more. I'm fairly new to Dane ownership, but have had dogs all my life.