For the wings: Heat a smoker to 250 degrees F. Toss the wing pieces with the salt and pepper and spread them on the middle grate of the smoker. Smoke them for 20 minutes, flip, and smoke for an additional 20 minutes. Remove the wings from the smoker and set aside.
While the wings smoke, make the BBQ sauce: Put the vinegar, brown sugar, ketchup, Worcestershire sauce, red pepper flakes, salt and pepper in a small saucepan and bring to a boil over medium-high heat. Reduce the heat and simmer the sauce until it is reduced by 1/3, about 20 minutes. Cool to room temperature.
While the wings smoke, make the dip: Combine the sour cream, green onions, feta, buttermilk, parsley, garlic, salt and pepper in a small bowl. Set aside.
To finish the wings: Heat about 4 inches of oil to 375 degrees F in a large, wide heavy-bottomed pot over medium heat. Working in batches, fry the wings just to crisp and reheat them, about 2 minutes. Using a slotted spoon, transfer the cooked wings to a bowl. When they are all fried, toss them with the BBQ sauce, and then serve with the green onion dip, carrots and celery sticks.