It should work - provided that your CF disk to IDE adaptor does follow the ATA-4 standards fully, and can operate at UDMA mode 4 (ATA-66) and MDMA mode 0.
I think that OPL allows you to select the data transfer type and mode, but HDLoader will run the disk at it's "normal" (maximum for the PS2) speed - UDMA mode 4.
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS