netmeg - 12:28 pm on Aug 1, 2013 (gmt 0)
Either way, my own perfunctory experimentation suggests that g### does not, in fact, index the 404 page. They may not even read it; once a robot has seen the 404 it can choose not to look at the accompanying HTML.
That's my take on it too, but since it's yet another thing I don't want to have to worry about, and since it takes minimal trouble on my part, my custom 404 pages are all no-indexed. (Kind of a forest meet trees thing)