Thank you aLTeReGo and Karlo.Zatylny.
Volumes do not have typical status indicators, which is likely the cause of the confusion.
Is there a reason for that? A basic Orion object not having (or at least displaying) the very basic Orion functionality of up/down status?
One workaround for me was to create a group (dynamically queried) listing our critical volumes, and these volumes show green indicators (so far) - haven't tested what happens when they go down. What I really need though is access to uptime graphs. But still, is there a reason volumes don't show up/down and other states (like "not responding") in Orion? The next step is to be able to answer a question, "how long has it been down?", and "has it been down before?" - in Orion, same as with nodes, w/o relying purely on event logs.