I watched the first 2 hangouts today. I get the impression so far that DHH has such an issue with TDD because he ascribes certain dogma to TDD which wouldn't be so for anyone with a deeper understanding of it's purpose. I'm not saying he doesn't understand it - just that he thinks that it is more than it really is due to the hoards of people who don't really get it.
For example he said that TDD encourages extreme isolation testing, which results in mocking every single collaborator. I'd say that TDD does the exact opposite - given that part of the benefit of TDD (when it's appropriate) is the emergent nature of the low level design, then testing methods & classes in small components is necessary to get the most out of that emergent design. After all the crux of design is the way in which constituent parts will work together - not alone.
I actually stopped following the series because as you said, DHH had some preconceived ideas about TDD that were not quite right and were probably based on his own experience with developers who practiced TDD in a suboptimal way. After a while the discussion became an edification of DHH on the true meaning of TDD.