And I might have misread where your problems actually are...
Because oVirt was born on SAN but tries to be storage agnostic, it creates its own overlay
abstraction, a block layer that is then managed within oVirt even when you use NFS or
GlusterFS underneath.
"The ISO domain" has actually been deprecated and ISO images can be put into any
domain type (e.g. also data).
But they still have to be uploaded to that domain via the management engine GUI, you
can't just copy the ISO images somewhere within the files and directories oVirt might
create and expect them to be visible to the GUI or the VMs.