None of the BlacX have any RAID capability so it doesn't matter if the drive is RAID-friendly or not.
At a minimum, any RAID requires at least 2 drives. And it must have a RAID controller in the enclosure. This makes the multiple drives look like a single drive to the DVR. The BlacX Duet is dual drive but does not contain a RAID controller so even though it's only one cable (requiring the host to have a SATA port-multiplier-capable controller) the host software sees it as 2 distinct drives - which we know is useless for a DVR.
For completeness, the WD4000FYYZ is an enterprise drive and is RAID-friendly. The WD4001FAEX is a desktop drive and is not designed for RAID.
Can the HR line deal with RAID 1? Would this impact performance?