
The only major stipulation in joining is that the dragon must believe in Sikhism, Buddhism, Jainism, or Hinduism. How explicit one gets in describing that dragon's faith is up to you. Even practicing the religion's about morality qualifies as following that religion, I'm not picky.
xd For example, Parvati is a devout Hindu, she's even familiar with the Kama Sutra (no, I don't know how that transpired). Siddhartha, on the other hand, if you couldn't guess, is Godar Dragons' equivalent of the Buddha, which Parvati won't entirely get or accept, but she'll just consider him an enlightened prince and move on. Charity, duty, enlightenment, and doing what you perceive to be the right thing is common throughout the pack, and following these principles matters the most at the end of the day, as well as getting along, learning from each other, and the well-being of the pack and the caravan that hosts the pack.
The Hill Folk, btw, follow a worn-down version of Hinduism that relies almost not at all on ceremony and the caste system. It doesn't make sense when everyone is expected to care for the horses and drive the wagons equally on a daily basis. The only requirements to join the caravan half of Nirvana is to get an approved Hill Folk character. Yes, you'll still be getting approval from me.
xd