I haven't tried anything new to fix my issue (the 360 can "see" Zune's tracks which are stored on my Windows Home Server), but once in a while the problem will fix itself for a short time. It takes a long while for any of the lists on the 360 (Album, Artist, etc) to populate. Once it does, sometimes one of my MP3s will play. After that one, none will play. It is pretty strange.
For WHS users, I think it would be great it that team could add functionality the way they did for Windows Media Center. Somehow hook Zune into the WHS without having to install Zune on it (which is possible, but unsupported). That way I could play my Zune Pass music directly from the server.
Master Blaster (Halo 30), Rumble (Blue 8), Frenzy (Black HD 16)