It's something like this I'm thinking of, remember the y value in "x/y Rz" is a percentage of the width of the tyre, so the rolling radius of the 350z wheels/tyres is about 1cm different between the fronts and rears on rays with standard tyre sizes. Swapping both fronts and rears may be ok, but across an axle? I'm no expert, but surely that would be enough to cause extra use of the dif at the very least?
But you don't know for sure if it would cause the accident?
Where there's possibility theres liability