Note that hdparm only controls if/when the disks themselves decide to spin down; it does not control if/when Windows decides to spin the disks down, nor does it prevent them from being spun back up by Windows or an application or service accessing the disks, and the effect is (normally?) per-boot, not permanent. If you want to permanently alter the idle timer of a specific hard drive, you should consult the manufacturer.
An issue here is that DrivePool does not keep a record of where files are stored, so I presume it would have to wake up (enough of?) the pool as a whole to find the disk containing the file you want if you didn't have (enough of?) the pool's directory stucture cached in RAM by the OS (or other utility).