Nope, I never connected a display to the majority of my ARM boards and since OMV is meant to be administrated headless (using the web UI or SSH/shellinabox) I don't consider this being a problem.
If a ping nanopim4 works in your network everything is alright and you can access the box using http://nanopim4
BTW: NanoPi M4 as well as NEO4 are prone to undervoltage, OMV/Armbian uses more demanding settings than FriendlyELEC's offerings and caused by this the voltage available on the HDMI port might fall below the allowed 4.8V so no display negotiation might happen. Details: https://www.cnx-software.com/2…-b-type-a/#comment-560002
I can confirm - no HDMI output anymore. Using the regular armbian images without omv deliver HDMI output and even the original omv images. After updating the system the HDMI output is corrupted. SSH and everything else works fine. Just no HDMI output.