Will iTunes even play files using third party (DShow) codecs?
No; xiph provide a QuickTime plugin on their own site for iTunes.
My point is that offering yet another media player as the only option to play vorbis files is disingenuous at best and shows the complete lack of connection with users that a lot of open source is guilty of.
Hmm, OK. I guess I understimated the standard user, or maybe it was just hard to believe that a user would take the FSF's endorsement (since that is what it seems to me) too literally. I would hope that anyone that is interested in playing Ogg files would look for a solution that incorporates their existing solution (be it iTunes or WMP). However I do see your point, but then again it is FSF's choice to endorse whoever they want, be it a single project or more than one.
I will note however that they didn't say anywhere on their site "the only player that will play ogg files is VLC" but rather "there are many players that will play ogg files, the one we like is VLC".