Aashhh...I see the mistake made (I made it a couple of weeks ago myself).
There is Hitachi...and there is HGST. Hitachi sold it's hard drive business to Western Digital in 2012, while HGST is the result of that deal. It is a Western Diigital whollyj-owned subsidiary...but it produces drives which are not WD drives and completes with WD in the hard drive market.
"It was agreed that WD would operate with WD Technologies and HGST as wholly owned subsidiaries and they would compete in the marketplace with separate brands and product lines."
So there is a WD sub which bears the Hitachi name, but it doesn't make or care about the old Hitachi hard drives. It has developed a new diagnostic utility which has the limitation you ran into...it's not made for Hitachi drives, it's made for HGST drives.
The utility for HGST drives...is not designed for Hitachi drives made prior to the merger/acquisition...it is designed for drives produced by the new entity (HGST). It is called the Windows Drive Fitness Test. It is downloaded from the HGST site and is mistakenly taken by some on the Web to be an updated Hitachi DFT version. It is notl.
The old utility is called simply the Hitachi Drive Fitness Test and can be downloade from http://www.majorgeeks.com/files/details/ibm_hitachi_drive_fitness_test.html
I just downloaded each...the Windows DFT download file reflects WINDFT.zip, while the Hitachi DFT (the one you want) reflects dft_32.zip.
Naturally, neither the WD or HGST websites posted anything that I've found...to reflect the differences for their customers .
Follow the directions at MajorGeeks to use the utility to test your drive.