My $0.02
If this was a friendly competition where there was nothing but bragging rights up for grabs, then a code of conduct could be agreed upon by all of us. We could all ignore the times of anyone we thought was driving outside 'our' personal idea of fair driving. This is how many of the racing series worked in Forza. Everyone knew what was allowed and what was not. Since the events were created and controlled by the gamers themselves, a much stricter set of rules could be adopted, regardless of what the game considered 'cheating'.
GT Academy is a whole different beast. There are real prizes at stake here, including a shot to become a real race driver. The game itself defines what is 'cheating' and what is not. Consider PD to be the governing body in this case. If the game allows it, and doesn't disqualify you for it, then you are not cheating if you use it.
If I owned a racing team I would expect one thing. That each of my drivers did everything within the rules of each particular event to come out on top. If other drivers were using a runoff area of the track to maintain momentum and run faster laps, and the governing body of this event was allowing it, I would expect my drivers to do it as well. If they instead chose to take the moral high ground and therefore lose time and the race, I would be quick to replace them with someone who would. Conversely, if they 'cheated', did something to gain an advantage that was clearly against the rules set out by the race officials, I would replace them as well.
I don't think anyone likes the idea of taking unrealistic lines in a racing game, it goes against our very essence as race enthusiasts. However, any real racer will tell you that if it makes you go faster, and it is allowed, then it is fair game to everyone.
