I am not saying this is incorrect but if it is acceptable then it is a reversal of an IASG interpretation made for QS-9000. The interpretation simply excluded a non-reply as acceptable documentation of a customer waiver. There was a lengthy discussion on this at the time and it has, for years, been the interpretations of QS auditors.
Using the logic applied in the other interpretation, it seems unlikely the interpretation for TS16949 would change. After all, a copy of a letter to your customer is only documentation that you wrote it - not that it was actually sent to anybody.
I understand you only have one tier 1 customer and they are the only ones requiring you to be TS however, once you are certified to TS, all your automotive customers are covered under the TS requirements. It has no bearing on whether they require certification. All of your suppliers, supplying your automotive processes, must be a minimum of ISO 9001:2000 with a goal of compliance to TS16949. This would mean the waiver, if valid, would have to be given by all your automotive customers who use the applicable material.
I agree that suppliers outside the automotive portion of the business are not subject to the requirement. As supplier development is one of the "hot items" in 16949, I would be very sure before risking a major non-conformance.
Dave