I agree with most you say. For me the question was more "could the NSA gain access at Google?" instead of "would the NSA gain access at Google?". If the Chinese could gain access to version control from the outside, then the NSA being on the "inside" shouldn't face a lot more problems. Else they could always try it from the outside.

A lot of confusion seems to stem from "direct access" and "collected directly from the server" anyway. I personally don't believe the NSA would ever install a backdoor at Google. There are probably other ways that don't involve direct access that are more in compliance with the law (which should be the main focus).