Some performance cars come with built-in cameras, but i don't know if they could really be classified as a dash cam. I'm thinking things like that Corvette/Camaro Performance Data Recorder. You need to manually activate that one. It also overlays a bunch of stuff you might not want in a regular dash cam, since it is supposed to be used for track performance evaluation (speed, RPM, g-forces, gear, steering angle, throttle position, and brake pressure).

BMW also has built in dash cams in some models (and the more disturbing passenger cam). It auto saves a clip when it detects an impact (20 secs before the impact or something). Other than that, you have to manually save and it grabs +/-20 secs from hitting the button.