I've looked at porting OMV to Devuan a couple times, but the author of OMV has tied the majority of his code directly to systemd behavior.
It will require a fork and a lot of unwinding of hardcoded systemd stuff to get it going.

I think it won't work then. Thanks for info.

Haven't tried it but their colllectd .deb has a sysvinit script as well as a systemd unit file so it looks promising.

Why don't you experiment in a disposable VM and report back?

Didn't work. It gave this output:

Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
openmediavault : Depends: netplan.io but it is not installable
                  Depends: systemd but it is not installable
                  Depends: systemd-sysv but it is not installable
E: Unable to correct problems, you have held broken packages.
bash: omv-confdbadm: command not found
root@somepc:/home/user# rm /etc/apt/sources.list.d/openmediavault.list

Why don't you experiment in a disposable VM and report back?