Hey guys! I agree with Jeff "De Professor" Allen when he says everyone gets in an uproar, in email, you can't read body language and vocal inflections which are more important than we give them credit for when reading what someone means and if they are upset, or joking.
Now to the question at hand, I think it should be taught, but as stated, taught as incidental or accidental maybe. The thing to remember, I believe, as teachers if you know a technique then teach it. It may not work for you, but maybe there will be two or three or maybe even one student in class to which it will be a great technique. They may be able to pull it off 95% of the time. If I can't pull a technique off, I tell them honestly that I teach it, I have not gotten it to work for me, but they should play with it in training and become familiar with it. If it works great, if not don't let it be your first choice.
Another thing I tell my guys, and in fights I have found this to be true numerous times, when it comes to techniques and positions for them there is good, better, best, and then where-ever you find yourself. the majority of the time it will be where-ever you find yourself. You better be familiar with what you can do from that position or reference point, and improvise.
I have taught the arm wrap, but not necesessarily as a trap, more as a transitional move to buy you a split second and disrupt your opponents movements long enough to do something. Not a "go to jail" tech. as Hock would say. We will probably see people who say they have done it, and it works, then others who say it is no good. That's cool. I never thought I would get a kaputa kapala on a guy in a fight, but in one of my earliest altercations with a shoplifter, I pulled it off. It happened so quick that I realized I had done it afterward when I threw him, and had him on his back pinned. Now, I teach the Kaputa Kapala, I have never gotten it again since, but it is good to know it is in my repetuar if I need it.