Hey everyone!
Just had a major failure with my OMV-box. Both my system drives running in hardware RAID-1 died completely and I had to replace them (this was exactly why I did set up the mirror on those system drives by not having to replace one or another). However, I picked up my old Intel X-25 SSD and installed Openmediavault again. Now the tricky part; Would I be able to import and use my already created RAID-6 array with my new installation?
After some trial and error -> YES! 
Here's what I did:
Disconnect every single hard drive.
Pick a new system drive and connect it.
Install Openmediavault.
Install updates.
Change back to your original hostname on the box itself prior to installationm, if you have changed it. (dunno if you need to do this, the mdadm-tool can be tricky)
Shut down the computer.
Plug the hard drives which the RAID resides on.
Power on.
Log in to the console as root.
Execute the following command:
mdadm --assemble --scan --force
(you only need to use --force if your array is degraded or similar)
Hopefully it will succeed.
Now log in to the WebUI.
Go to RAID Management.
You should see your array, if not reboot and look again.
Go to Filesystems tab.
Select your filesystem(s) and click Mount.
All done! Everything should be back except general configuration settings like shared folder etc.
It's no guarantee that this will work, however it worked out for me.
I hope this can help others in the same position.