Cheating? It's difficult to come up with a definite answer, because it’s not easy to draw a line between what’s cheating and what’s not, for the same reason why it’s so difficult to explain talent or art.
Even when you do consider something cheating, you could ask yourself who’s being cheated; the viewer or artist himself?

Unlike the majority of the artists who seem to prefer references (don’t ask me why), I on the other hand prefer to use no direct references, whether it’s a photograph of even drawing from “life”. I find “carbon copy art”, because that’s what I call it, pretty unexciting and not only as an artist, but also as a viewer.
I want to create something out of nothing and have full control. Sure, that’s not an easy road, but I do like the challenge and really dislike copying from references, like for example working for 30 minutes on a mouth just to get that likeness right…sorry, I find that boring. In that same amount of time I could have created this unique expressions in the eyes that made the face really stand out.
I respect it when someone makes different choices, I just happen to have totally opposite ideas.