Hi Greg
I'll jump in here only cause you mentioned that you do Jodo, and we've already spoken. I don't know what your exact concept of a Sensei is, and like everything we all have different concepts.
In my case, I wouldn't so much see it as "permission" but rather "guidance". In the end who can truly tell someone else what to do, rather a good Sensei or what Nishioka Sensei calls a "master teacher" in his Shu-Ha-Rei: Uchidachi & Shidachi article will always lead by example and others will follow if they're worthy or if others desire.
IMHO it's a bit like your Father (you should try to only have just one for that particular art, or style.. armed or unarmed), in this way it's not a democracy in his house.. but at the same time it's the nuturing guidance we all seek and admire, in an effort to improve ourselves both technically and spiritually.
Others can see it as a Military system, rather than a family one. Again, each to his own.
And most teachers I know would not have a problem, letting you do an unarmed art some even suggest it, the same for external Seminars.
Cheers
Greg
Greg Clarke
清隆会 Shinto Muso Ryu
兵法 Niten Ichi Ryu
"Seek out the middle of the two we's in I"