I'll use whatever I can, whenever I can to try and get down what I'm seeing in my head, and if that's cheating, I don't actually care. If I enjoy doing it, and I'm happy with the result, then winner winner chicken dinner as far as I'm concerned. Do what makes you feel good.
I tend to make a basic outline stencil to get the general shape and position of things, or do a light pencil drawing, and then freehand the details, but I'll use masks, french curves, objects from around the house, or whatever, if I think I need to.
The only thing I consider cheating is someone not fessing up to copying someone elses work. I think most people copy, borrow or adapt to some degree I know I do, and I don't see a problem with it, but if someone copies and then try to pass it off as thier own, then I think that's cheating. But that's just the opinion of little old me.