I've been watching some replays of the top times, and I noticed a lot of people are using the grass as run off in turn 6 as they head under the bridge. And it's not like there car's just sliding off for a second, they purposely keep it out in the grass for nearly the whole straight before entering turn 7 (The flat out corner).
Now, if I remember correctly, last years GT Academy was held up due to people going off into the grass because it gave them an advantage. Now, putting your car on the grass in this years GT Academy is giving you an advantage as well. However, PD put cones where they didn't want people going off into the grass. So, either they don't care you're using the grass where they didn't specify you couldn't, or, they didn't think anyone would bother to use the grass there.