Even film cameras? It seems like the only latency with those is determined by the speed of light. From what I can tell the light you see in the eyepiece is pretty much happening in real time due to it not running through a computer. But if I'm wrong, I won't complain.
Spinning shutter cameras would off by an "inbetween" frame (you see when the shutter is closed, not when the film is being exposed). Beam splitter or parallel viewfinders would be true 0 latency finders.