I'm intrigued. My two cents (if you haven't brewed already) is to leave out the late hop additions altogether and drop the black patent. Use a bit of roasted barley, or even derive all the color come from the less harsh carafa malts. Seems to me a Nutella stout should let the chocolate and hazelnut shine by putting bitterness, hops, and roast flavors to the backseat. With that said, will you get hazelnut flavor after removing the oil and only mashing with them, rather than boil or secondary?