Unless you'd rather just restart the game from the beginning every time, I wouldn't count it as cheating. I mean, if somebody can sit down and go start to finish without having to redo an area then good for them, but I know I can't do that (at least not without some serious memorization of enemy movements and practice) so I'd settle for the next best thing, retrying areas where I was spotted.
It'd probably be wise to save in every area so if you're spotted, you wont have to start again from that far back.