Mr. Monkey,
Unfortunately you neglected to mention the Law of Partial Pressure of Gases (also known as Dalton's Law) that states that you can treat a mixture of gases (like air) as though they were individual gases. So at sea level, where the atmospheric pressure is 14.7 psi and oxygen is 21% of the mixture, 02 has a partial pressure of 3.1 psi.
What happens is that oxygen will flow through the tire, into the air chamber as though there is 3.1 psi pure oxygen on the outside, instead of an air mixture - in spite of the nitrogen flowing out.. Yes, this has been verified.
So, No, the rubber inside the tire gets to see oxygen, but at a lower pressure than if the air chamber is filled with pressurized air. And, of course, when the oxygen combines with whatever it combines with in the rubber, the partial pressure insures that more oxygen is moved into the interior of the tire.
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