All I've tried to update OMV in normal ways failed. I thought when I connect one of the raid drives to an linux machine (Debian 10 in my case) I'll be able to access the data stored on, but it doesn't work either. That's sets me back and let me think about a new/other NAS solution.
This should work indeed because OMV does no magic when the RAID is created. It's like other distros suggest it in their howtos. The only thing you need to do on another system is to activate the RAID to get it working.