In emergency situations, vehicles tend to pivot around odd tires - and the more different the tire, the stronger this tendency is. Unfortunately, you can't tell how strongly this is going to be unless you either test 9which will destroy the tires, thereby solving the problem!) or until you have an emergency situation (and that means it's too late!)
This situation is about about as bad as it can get - P metric vs flotation. I'll bet the brands are different as well. On top of that, there the severe rainfall problem.
I think this is about as risky as things can get, short of 10 year old tires driven at 80 mph. Again, the problem is when there is an emergency. You'll just never know when this may come to bite.