Very interesting! However, the listed pronunciation is not correct. First, the "Nee-ee" part is correct, so Niihau is more accurately written as Ni'ihau. The glottal stop, called an 'okina, indicates that there is a pause between those vowels. Second, in Hawaiian, "au" produces a sound roughly like "ow." Therefore, Ni'ihau is pronounced more or less like "Nee-ee-how." If there was an 'okina between the a and the u, THEN it would be approximately "Nee-ee-HAH-oo."