I think you have everything you need. The fact that your OMV system can't resolve the hostname at mount time is why it can't mount the remote mount. You could switch the remote mount to use the remote system's IP address to see if that fixes the issue.
I just changed Remote Mount to use IP addresses instead of hostnames, and I see a new error on boot:
Oct 19 10:09:11 omv kernel: CIFS: Attempting to mount \\10.0.0.20\video
Oct 19 10:09:11 omv kernel: CIFS: VFS: Error connecting to socket. Aborting operation.
Oct 19 10:09:11 omv kernel: CIFS: VFS: cifs_mount failed w/return code = -101
Oct 19 10:09:11 omv kernel: CIFS: Attempting to mount \\10.0.0.20\music
Oct 19 10:09:11 omv kernel: CIFS: VFS: Error connecting to socket. Aborting operation.
Oct 19 10:09:11 omv kernel: CIFS: VFS: cifs_mount failed w/return code = -101
Looking further down the logs, that's happening a few seconds before dhclient performs DHCPDISCOVER on my ethernet interface:
Oct 19 10:09:14 omv dhclient[582]: DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 12
Oct 19 10:09:14 omv sh[582]: DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 12
Oct 19 10:09:14 omv sh[582]: DHCPOFFER of 10.0.0.10 from 10.0.0.1
Oct 19 10:09:14 omv dhclient[582]: DHCPOFFER of 10.0.0.10 from 10.0.0.1
Oct 19 10:09:14 omv sh[582]: DHCPREQUEST for 10.0.0.10 on enp3s0 to 255.255.255.255 port 67
Oct 19 10:09:14 omv dhclient[582]: DHCPREQUEST for 10.0.0.10 on enp3s0 to 255.255.255.255 port 67
Oct 19 10:09:14 omv dhclient[582]: DHCPACK of 10.0.0.10 from 10.0.0.1
Oct 19 10:09:14 omv sh[582]: DHCPACK of 10.0.0.10 from 10.0.0.1
Oct 19 10:09:14 omv avahi-daemon[632]: Joining mDNS multicast group on interface enp3s0.IPv4 with address 10.0.0.10.
Oct 19 10:09:14 omv avahi-daemon[632]: New relevant interface enp3s0.IPv4 for mDNS.
Oct 19 10:09:14 omv avahi-daemon[632]: Registering new address record for 10.0.0.10 on enp3s0.IPv4.
Oct 19 10:09:14 omv dhclient[582]: bound to 10.0.0.10 -- renewal in 1406 seconds.
Oct 19 10:09:14 omv sh[582]: bound to 10.0.0.10 -- renewal in 1406 seconds.
Oct 19 10:09:14 omv sh[1280]: enp3s0=enp3s0
So OMV is trying to mount the Remote Mount CIFS shares before networking is up, which is why it is failing at boot.