MIchael, I had something very frightening happen to me last night. I've been running 10.7.4 for about 2 weeks without any change in my issues then suddenly and for absolutely no reason, I lost all access to my OD. No user accounts could log in to the network, no accounts or groups appeared on the server, and I couldn't add either if I wanted to.
The only option I had was to rebuild from scratch because I never bothered to do a back-up since things were so hosed in the first place. Fortunately I don't have anywhere near the number of users you have, unfortunately I don't have the knowledge of networks and server that you have, so I made my solution a little simpler. Here's what I did;
First I demoted then promoted the server. (I also threw in a couple of reboots just for good measures. 😉).
Then I recreated each of my accounts and groups. Again there weren't many so it wasn't much of a task.
My accounts were then able to log in but no one was able to aceess their files. With a little digging in these forums I found the chown -R username path command in another post. I tried using it just like that but it wouldn't work. I crossed my fingers an used the sudo command and everything worked fine. Not thinking I tried using the chown with a local administrator account. Should I have used the diradmin account instead?
Anyway, for whatever reason that worked. What makes me mad is I tried this exact same process about two months ago and it never solved my problem. It was only after the OD completely blew-up did it work. I feel like everything is working as designed so I made back-ups of my OD. I'll update if I ever need to go back to them.
--Dave