levo - 7:05 pm on Nov 26, 2012 (gmt 0)
No worries, there is no information/documentation on how Googlebot discovers and subscribes to the pushed feeds.
The only clue I can find is, you can't diagnose your feed without any subscribers, and once you add it to WMT, diagnostics works. So, I assume Google(bot?) subscribes to push notifications once I add the feed to WMT.
Why would you add the full RSS as a sitemap (and risk that I just might be discovered by scrapers, too) if Google only reads URLs from sitemaps?
Is there a risk? Can someone find feeds that I've added to WMT?
BTW, I use "X-Robots-Tag: noindex, follow" header for feeds.