I'm having a similar issue. Mostly on Linux boxes. I haven't really tried too hard with OSX just yet. I posted my problem in the forum. The issue is related to how mount.cifs mounts home dirs as well as other shares with the forceuid and forcegid options with no way to change then. Have you managed to get this working in that use case?
I'm not really sure what OSX uses for CIFS. Maybe Samba as well?