I was in for a short time a couple years ago. The application process takes about 1 year, and it'll involve a few trips to Hawaii. HPD helped one of my classmates on the mainland to consolidate the interviews so she could do less trips here. The exam was grammer and spelling, and there was a memorization test where you had to read something, paragraph and a list, and answer questions without looking back. If you have military service, they will add your veterans points to your test score.
I hope you have spent a good amount of time in Hawaii. The lifestyle is different and there are some places on the island where you may have trouble as an outsider. Most of your cases will consist of homeless, meth heads, and crazies. I have no experience with departments except for HPD, but it seems like policemen here are very isolated from the rest of society.
Pay is good compared to other jobs in Hawaii especially with the overtime you'll collect. However other mainland cities do pay more. Update on the COL, average selling price of a house last month was $977,000.