I wrote kaleo works IN oʻahu.... should be correct.. I/ma = in, on, at
O'ahu can be thought of as a place like a city or a province instead of just an island. When we talk about what city or maybe province or state where someone works, we say "work/s in'. "He works in Berlin." "I work in California." Even for a country, we'd say "They work in China." I think the verb "work" is the key to determining the preposition here. (Not saying that "on" is incorrect, btw, just saying that I don't think "in" is wrong in this context. We obviously don't stand in an island. Taken literally that boggles the mind.)
1 nCap. Name of the most populous of the Hawaiian Islands and the seat of Honolulu. The name has no meaning (see Pukui, Elbert, and Mookini; 1975, 262). See saying kau poʻohiwi, and epithets, Oʻahu (English-Hawaiian). [PH]
1 prop nCap. Most populous of the Hawaiian Islands, 40 miles long, 26 miles wide, with an area of 608 square miles and a 1970 population of 768,561. Honolulu is the major city and State capital. See Appendix 6.8 for a refutation of a meaning often quoted, 'gathering place'. Epithets: Oʻahu o Kākuhihewa, Oʻahu of Kākuhihewa (an ancient chief); Oʻahu a Lua, Oʻahu [child] of Lua (Lua slept with Papa after Papa became angry about husband Wākea’s infidelity; Lua gave birth to Oʻahu; HM 302).