This is early stage of testing only. Use at your own risk. Your mileage may vary.
Update 9/2019 The script works on OMV 3, 4 and 5. With windows server 2008, 2012 and 2016. Maybe others?
Seems to be quite a few threads about this over the years. I have had it working for years but it seems to be quite tricky. With 3.0 coming I decided to look at it again. I did not test against 2.x but it may work as well. I started clean and found something I had not seen before, sssd. It seems to do both AD and other ldap well. I only have a 2008 server to test with so please test other variants if you are interested. I test this in a proxmox vm against a 2008 sbs server with only a few users. I am pasting my notes and hope they are readable.
I start with a clean install from the iso of a few days ago.
The ultimate goal is to get sssd into the code or at least as a plugin. Another useful tool may be realmd, I have not tried that yet.
I hope this is of interest to others.
Added a script here. script post