Hawaii has special problems, temperate climate with no seasons. There is a American Rhododendron Chapter in Hilo, Hawaii. It can be contacted at:

tropical@greensand.net

They have a list of "Proven Performers" at:

http://www.rhododendron.org/performers5.htm

The list is all Vireya Rhododendrons which are subtropical and tropical plants originating from places like Borneo and New Guinea. The recommended varieties include:

'Aravir'
'Birat Red'
'Calavar'
'Candy Halo'
'Charming Valentino'
'Cristo Rey'
'Dawn Chorus'
'Doris Mossman'
'Elegant Bouquet'
'First Light'
'Great Scent-sation'
'Haloed Gold'
'Harry Wu'
'Highland Arabesque'
'Humbolata Bay'
'Java Light'
'Jock's Cairn'
'Kisses'
'Littlest Angel'
'Lucie Sorensen'
'Mount Pirie'
'Narnia'
'Popcorn'
'Saint Valentine'
'Simbu Sunset'
'Sirunki Lake'
'Taylori'
'Tropic Glow'
'Vladimir Bukovsky'

A source of such plants is:

http://www.pacificislandnursery.com/

Here is a link that might be useful: Hawaii Chapter of American Rhododendron Society