No harm in asking. Just don't expect a wealth of positivity for that particular art on this particular forum.
And you really should read through the thread ashkelon linked.
Normally, I'd be the first one to crack on a Ninja (if they really existed that is), but since everyone already beat me to it. Welcome to Bullshido.
As far as your "longstanding interest in Japanese arts" and your desire to learn "the principles and 'secrets' of Ninjutsu", stick with aikido. The "form and function" of the taijutsu's similar and you can get your fill of Japanophile mysticism without your instructor trying to saddle you with the delusion that what you're training has any practical value.
Here is a recent thread that will cover EVERYTHING he wanted you to understand:
Japanophile, yes, mystic... probably not. I do practice Shinto, speak passable conversational Japanese and have trained in Japan.
I have no intention of quitting Aikido after 30 years, I do however want to further diversify my combat skills. Having practised Iaido almost as long as Aikido, I'm interested in the weapons training. As Hatsumi is technically a Samurai as well as a "Ninja", I figured not all of it can be pseudo mystical BS.
I wrongly assumed that people here would be open to discussion and debate. Everyone seems to be constantly fighting their own little war of words.
Let the verbal Randori commence!
I have read the recent thread and it answers some things, but not all. I'll go back to Google for that.
Sorry for coming across as an asshat, I'm an ex-Squaddie and can be a little too aggressive sometimes.
BudoCanuck, after 30 years of Aikido training I think you're probably more knowledgable about Japanese martial arts than most people! We have a pretty awesome JMA forum here on Bullshido that is fun to scroll through. What sort of aikido do you practice? Did I glean correctly that you're also an instructor?
I practice Yoshinkan, and I was a "hand to hand combat" instructor in the British Army (mostly basic Aikido, Systema and Krav Maga), but I have never officially taught Aikido in a club Dojo setting.
A personal choice for various reasons, but that may change if the opportunity arises.