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Fail. I took a semi-extensive Japanese history class.
And Ninjas, or Shinobi, were very simply hired mercenaries who specialized in sneaking into enemy territory. To find gaps for an army to enter, set fire to the castle, gain information, or to carry out assassination.
They're training mainly consists of sheer survival skills. Thus, any hint of religion would have been a very primal one, and there is absolutely no history of a connection between monks and the Ninja.
They were hired by whoever could afford them. So, mainly the Daimyo. Who were rich lords who owned a lot of land.
They weren't good Samaritans, if that was your impression.
I'm sure there were some chaste ninjas, but they would've chosen to be so for very separate reasons, and NOT because of their profession.

always tryin to compete fenny. neutral tsk tsk tsk. IF ONLY yuu can be like me and not always try and trump someone ninja

Fail. I've devoted an unreasonable amount of my free time for past several years, to studying Japanese culture and history.
You're thinking of Samurai. Samurai and ninja are NOT the same thing.
Truth be told, the existence of ninja's is still speculative, as accounts of them are few and far between. Some people think they were martial arts masters of the Asian mainland, while others think they were monks who developed their combat abilities as part of their religious lifestyle, and some other people believe they were just a folk tale based off the factual Samurai.
One thing that's generally accepted (should ninjas have existed) is that they weren't upper class citizens. Most of them were probably broke. In other words, even if they weren't chaste, NO CONCUBINES.