Aloha hou mai kaua:
Up until recently I did not know that Hawea even existed, but I heard about it in regard to some construction damage and general hukihuki over the site. See this recent article, for example:
I am not familiar with the heiau personally, never visited it, but in general I have great aloha for any heiau that still exist in todayʻs world, and I am glad you are following up and visiting the place. I would be able to advise on what plants would be approrpaite for the vicinity, though I would also have to visit to get a better feel for the conditions there. Being close to sea level, in a low-rainfall area, and close to a wetland, that would frame the kinds of plants that could be found in the area.
I know this is not much help, but you may find more if you search for recent articles on Hawea to be found on the internet.