Are there any special hardware requirements to take advantage of the Darkive feature?

This requires power management features that are standard on mainboard and hard disks for at least the last ~8 years, so not really.

While there are no special hardware requirements for the Darkive feature, the specifics of the actual hardware can greatly improve the overall power shed of the system when Swarm allows the disks to go idle. This is something that is normally published in the hard drives' specification sheets.

Swarm "leaves the disk alone" so that it can do whatever it does to go idle. On SATA disks that aren't behind a RAID controller's virtual volume, we issue the arming command that tells the disk to spin down after a few minutes of being idle.