I don't know anyone who pretends to be Japanese. I do know that O Sensei wanted every student to wear hakama. There are stories about students who could not buy a training hakama so they borrowed expensive dress hakama from family members and ruined them in training. Was it not O Sensei who thought of the keikogi as underwear?
Well, he talking to primarily Japanese students training in Japan. When I'm in Japan I generally bow and speak Japanese. When I'm in the US I generally speak English and shake hands. Isn't that the way that it usually is?
If someone's attending school in the US then I'd expect them to follow the normal customs of whatever US region they're studying in while they're here. I wouldn't expect them to go back to Japan and teach their students to shake hands with each other in order to study mathematics.