I am able to convince iTunes to play flacs/oggs locally, albeit it's a pain. Well, not that painful. Two components have to be added into separate system folders.
However, when iTunes connects to a DAAP share from my Ubuntu/Rhythmbox machine, flacs or oggs are seen but misunderstood.
The playback solution from my disorganized post above gives QuickTime the ability to play flacs and oggs. The problem is that iTunes won't use QT for flac/ogg playback unless you add some metadata to the resource fork for an individual file. Never will happen for a non-local file.
DAAP, being non-local by nature, cannot participate in this slight of hand. Unless...