you can see the ML overlays on an external hdmi monitor. BUT be wary if you shoot raw video since the crop marks for raw video is still buggy for current releases and is not properly displayed.
If you will be recording raw video and using external monitor, you will want to turn off the preview framing guides and probably just mark your framing on the monitor with tape or acetate etc.
Also, when recording raw video, do not preview your footage or play it back with hdmi attached as it will freeze your camera and you will have to remove the battery to unfreeze it.