Yah I've seen it. It is not very practical. If I have that arm between my legs I'm looking ot belly down on it rolling onto my right shoulder so that I can kick him onto his back with my left leg.
In the video hooking the leg with your leg will put the arm at the wrong angle and make it very difficult to maintain control for the armbar.
Also, I find it unlikely that anyone would willingly leave their head down there.
