Also, if I understand it correctly, there are a few other caveats with hot spares: It will only activate when another drive completely fails, so you can't decide to replace a drive when it's close to failure (probably not an issue in this case, though, with the unresponsive drive). Second, with the hot spare activated, the pool is still degraded, and the original drive still needs to be replaced; then the hot spare is removed from the vdev, and goes back to being a hot spare.
It's these reasons that I've decided to just keep a couple of cold spares ready that I can swap in to my system as needed, although I do have access to the NAS at any time. If I was remote like GP, I might decide to use a hot spare.
But a disk can only be a hot spare in one pool, so to have a "global" hot spare it has to be done manually. That may be what that poster was doing.