I've seen a lot of fast FWD track/autocross cars and most of them ran so much more front camber than rear that you could eyeball it quite easily. It might reduce understeer running excessive camber in the rear, but you're achieving it by essentially reducing the rear contact patch, which I would argue is the wrong way to do it. If GT allowed positive camber I'm sure running positive rear camber would achieve the same result, but this would also be a bad idea for obvious reasons.