On a compliant or completely untrained or unsuspecting opponent ok.
Pull this off in the manner it is shown on an opponent who is fighting back or at real time vs real punching and counter punching. Can this action be performed at real time on a person who is punching or countering? Yes it can, but not in the manner it is shown. One doesn't have to go hard or fast to demo but at least the timing, footwork, body positioning, and angle of attack should be proper. The opponent can be compliant for the demo but should also be attacking and countering properly in that when an action, such as in this video, is performed poorly or improperly even the untrained can see/tell what does or doesn't work and why. A simple forward movement with a Quan Sao action (which the attacker is actually giving by turning the arm as he stated in the video) will prevent the attack.
I understand wing chun and I understand dumog. I understand demoing. I also admire all who put themselves out in video for the criticism. In this demo I'll give it may work due to the simple mass difference of the two and the total compliance of the counter. But vs a real counter-attack I have to disagree and vs one who may have a weapon in either hand and is attacking; 'It ain't going to happen!"