A couple things:
First, with the following comment:
I was not addressing you, lucid3ye.
You have a different set of circumstances, that does not include "raspi-config", so I don't know why or where the snark is coming from. But I will say this; it's not helpful when forum users inject themselves into the middle of a direct conversation with a specific user, with quotes and comments that don't apply and snark added as garnish. Problems are not dealt with by "piling on". They're solved one-at-a-time.
In any case, I did the test run and found what appears to be a systemd network issue.
Having cut my computing teeth on a Commodore 64 and DOS 1.X, 2.X, etc., I seriously doubt that you were building systems when I was in diapers. In my diaper days, "a computer" might have been crossing over from tubes to some of the very first, experimental, TTL circuity. Building a system at that time would have taken the equivalent of a tractor trailer van full of equipment, DARPA PhD's (ARPA at that time), a ton of money and resources.
Further, having been retired for a bit over 13 years now, it's possible that I may be older than you are.
You followed an install guide for OMV 6.0, to install OMV7 RC1. Had you followed the install for OMV 6.0, as it was written, OMV6 would have installed flawlessly. (Absent hardware problems and user induced mystery issues.) OMV7? Obviously, there are no guarantees. At the moment, I'm working on the OMV7 install guide for AMD64 ISO - one thing at a time.
With the above noted, if you think you can write a guide for installing OMV7 on R-PI's that's succinct, not confusing for beginners, that will support broadest cross section of users (beginners and enthusiasts alike), and you're willing to support it, please feel free. I'll even publish it on the Wiki for you, so you won't have to go through the Markdown and HTLM learning curves.
You see, the support angle comes with trying to figure out hardware issues, build problems, and how users go off the beaten path. The latter, not following instructions or deviating without admitting it, is easily where +60% of installation issues come from and it's where a LOT of forum time is wasted. (As forum contributors look into the "crystal ball" of their expertise, experience and intuition trying to figure issues out, remotely.)
___________________________________________________________________________
Reading through your posts, it appeared that you might have a DNS issue which might indicate a problem with your local router, the router's configuration or your DCHP server, if it's separate from the router. (This is what I was talking about when saying you have a different set of circumstances.)
Local hostname lookups have very little to do with your R-PI (assuming it's not being used as a DNS or DHCP server). If you have local DNS, you could misname the R-PI's hostname and it's domain suffix, in OMV, and it wouldn't matter.
You can setup a crude form of local DNS by:
1. Setting up static DHCP leases for the IP address(es) of your server(s) which should include their hostname(s).
2. In my setup, I statically address my OMV servers with the same IP address used for their static DHCP leases.
(While optional, static server addressing eliminates a server's reliance on network connections and an external, DHCP, process.)
When clients do a hostname lookup, the local Router/DCHP Server acts as a local DNS and returns an IP address. This has worked well for me. It might work for you.