Just for general information in the last weeks I made some new install on DX4000 units and I found some information which might be useful to share.
First of all I came across a WD Enterprise with the following p/n: WD4000FYYZ-01UL1B3
A similar one is included in one of the whitelist.xml files of the latest firmware (01UL1B0). I tried to modify the whitelist file but I did not manage in any way to start the RAID rebuild or OS recovery process with these drives. I always got errors at the end of the recovery process with the USB memory sticks created with last distribution (v220.127.116.11) . However it looks like this drive can be used as replacement in case one of the other fails provided the WD drive enabler is installed. At least the recovery process started after having exchanged one of the original hard drives with this one, still have to check it is successfully completed.
Another interesting information is related to the functioning temperature of the drives. I added two RED NAS WD drives to an existing installation with 2x 3Tb drives (Enterprise, the official ones which appear in white list) also in this case after having used the WD drive enabler utility. The WD RED drive temperature is 5-6°C (10°F) lower than the corresponding enterprise drives which always reach and sometimes exceed the 50°C level. My gut feeling is that WD RED drives have much better thermal management than the Enterprise ones which were the mandatory option on the DX4000 (at least till the WD drive enabler appeared).
It is really a pity that for a first install you have to rely in any case on the Enterprise one, as the WD drive enabler can only be installed afterwards.