The Ainu portrayed in the film are an indigenous people who primarily live in Hokkaido, the northernmost Japanese island. Up until the late 19th century, both the Ainu and Hokkaido were referred to as Ezo.
Kamui Nupuri means "great mountain" in the Ainu tongue. The word "kamui", also romanized as "kamuy", usually refers to animistic deities, but when preceding a noun, it acts as an intensifying adjective for it. If the name was Nupuri Kamui, the name would mean "mountain god". Kamui may also be a cognate for the Japanese word "kami", which has a similar usage.
Captain Kidd's treasure ship was finally found at Santa Catalina in 2007, but not at the one located off the coast of California, as was depicted in the film. Kidd's ship was found thousands of miles to the east in the Caribbean, off the shores of Catalina Island, in the Dominican Republic. The island was originally called "Santa Catalina" by Christopher Columbus when he discovered it in 1494.