That is correct. With EQL once a drive is marked as failed, it will remain failed until it is replaced. Then once it is replaced it will take the spot of the hot spare that rebuild into the array.
I have a EQL PS4000X that had a disk stop working, it did fail over to one of the hot spares i had setup but when i removed and replaced the disk it didn't fail back as you describe that it should. I have not found a way be sides ejecting other disks that would get the disk back active again to see firstly if it is now ok or if it is indeed actually dead and requires replacement. are you able to advise that if there is a manual of bringing the disk back online?
HDD Failback PS4000X