Can Nikon lens automatically follow the focused video? Is it effective?

Yes, but follow focus's performance is not very good. Not as good as Canon dual-core focusing.

But then again, how many people who shoot video with SLR can use autofocus? Single-lens reflex shooting video is for the sake of fine carving of image quality, similar to film cameras, but different from camera quick recording. A really serious photographer will give the SLR a kit (also called a movie kit), which will have a follow-up focus unit. The photographer will manually follow the focus or let his assistant (follow-up focus) follow the focus. Therefore, autofocus is rarely used when shooting video with SLR or micro-camera.