Secondly, I'd be impressed if after the China incident, you still had access to Ads mailing lists given that you work in Search, so it at least seems unsurprising that your searches would reveal nothing.
For example, I often see disgruntled publishers complaining on the web, and from time to time I've followed up on specific blog posts to get the other side of the story. In addition, the group that manually fights webspam at Google is a sibling organization to the group that fights adspam.
Finally, I passed these claims directly to the ads side and so far I've gotten three (now four) different "this is fake" responses from people I trust and have worked with in different capacities for years, including an engineer that I worked with in search quality who later went to work in ads.
What is one to do in these treacherous times? The same thing you do with every other interaction you have with people. Weight the information provided with credibility factors based on context, delivery, bias, historical data about the source etc etc.
Either Mister Cutts has built up credibility for you over his many contributions, or he has not. That's your call.