I'm not sure if I believe them when they say that the gluten has to be ingested. They claim that the protein is too large to pass through the skin but I read stories here and there about people having to make sure they switch to a gluten-free soaps and shampoos after going gluten free in order to avoid rashes.
The medical establishment seems to know so little about gluten reactions that I wouldn't be surprised if they focused only on the damage being done to the small intestines when they say that skin contact wouldn't have any effect.
I used to break out in hives on my hands and get rashes on my wrists back when I was still consuming gluten, but only here and there. Of course, I can't remember the meals back then, but I have to wonder if it was from when I ate foods that were picked up rather than eaten with utensils. I can tell you that I don't risk it these days.
I definitely react when I breath in dust in the air that contains gluten, which would be a problem if you worked around flour. For me, it just feels as if I have a sinus infection, lots of pressure in the cheeks and forehead and some ear aches, plus a little more phlegm production overall. But I've also never had DH as a symptom.