Well I don't have any definite scientific answer to whether it's the dryness or the temp that makes leathery poultry skin.
All I can say is that I get edible skin out of the smoker when the temp is 325F the entire time. After pulling leathery skin chicken out of the smoker I've tried to blast chicken in the oven on broil for 10 minutes but that didnt work, I've tried a propane torch and that didn't work.
May report that they grill on a hot grill (like 600F) and char the skin up some and that works for them.
Also some like Foamheart put their chicken under a fan until a pellicle forms and that works for them so dryness can factor in. Others have reported using cornstarch on the skin to dry it up before smoking. I have not tried either approach so I can't tell you anything about them other then people mention them.
So I guess from my experience I can say that the smoker temp will definitely affect the poultry skin texture and I have edible skin at 325F and with my convection fan mod in my MES I've even had crispy skin occur. Smoke at 325F or higher and I think you will be ok.
Let us know how things turn out :)