Yes, it is based on retirement rank, and you need an ID card to show you're eligible. There is also a listing of other folks who can use the facility, The website has a really easy to use listing of who can and who can't....There are even some NATO personnel that could qualify.
Worth the look if you ever think you might go to Oahu for a holiday.
If hotels are not your favorite way to travel, the beach houses at Bellows and NAS Barbers Point are also available to retirees. Have used both Hale Koa and Barbers and find both are great values. A former Marine tells me that the same is true of Bellows.