You'd think so, but not with Schiit. If you're willing to take the risk, have a source playing into a Jotunheim, listen to it with headphones, turn the Jotunheim's switch off: instant silence. Turn it back on, you'll won't hear music until it's considered safe. Now pull the plug or cut power differently upstream: you'll keep hearing something for a bit. Put the cord back in, you'll probably hear music sooner.Power switch at one end of the cord or the other makes no difference.
The muting function for protection seems to require (and get) power even when the Jotunheim's switch is off, at least that's my guess.
I asked Schiit about using a smart plug a long time ago, and was told "I wouldn't recommend using it in that manner. The Jotunheim has a muting relay by design to prevent sound coming through immediately for safety."
Asking whether the same is true for Vidar and Freya, I got "That is correct."