It's certainly plausible that the drying process is mutagenic -- drying is stressful, and mutations increase with stress. But then, getting sealed in a plastic tube or smack-pack and shipped halfway across the country is also stressful.
What I don't get is, why bother? The whole beauty of using high-quality dry yeast is that it's simple, and that you don't need to mess around with culturing, storage, starters, etc etc etc. Unless you really love doing that why not just buy more dry yeast? And if you do love doing that, there are lots more interesting yeasts to do it with than US-05 or Nottingham.