Well, I just checked little Grendel over and saw no sign of irritation (beyond shaking his tail at me for daring to scoop him out of his house, home wrecker that I am.

). His skin is uniformly white under black fur, though he had 'dandruf' that could also be from the aspen chips. He also shed a few hairs while I had him in the bathroom, but I was back brushing his fur with my finger, so I might have just shaken out some loose ones.
I'll keep checking him for the next few days, but he hasn't been away from his litter long, so the sudden behavior change could just be adjusting to having 5 gallons of fun to himself. Right now he's digging through his bowl for the sunflower seed at the bottom, so I don't think he's mad or otherwise out of sorts. Thank you both for the input. I'll update if there are noteworthy developments.