The DVO has been removed with TEDAC, yes. While DTV is a tv camera which sends a tv signal which is processed and shown on a monitor, the DVO was a pure optical sight, like a sort of telescope. It used just mirrors and lenses. The only way to view its image was to look through the sight which used to be in the center of the CPG's cockpit. The pilot had no ability to view the DVO image. I hope this helps explain the difference between DTV and DVO.
As a curiousity, the DVO, and similar optical sights is the reason why the gunner sits in the front seat in most helicopters. It would be too cumbersome to make the lenses&mirrors sight in the nose go to the rear co-cockpit. However, some newer helicopters, like the Tiger, and cancelled Comanche have the pilot in the front seat as they have discarded the optical sights, and have just cameras.