We have native hibiscus trees. Ours is in endemic rainforest and is the same colour as in image below. They are quite spindly, perhaps slender would be s more flattering description, with their trunks about the size of a broom handle. I have seen them used with syrup, as you mention, in local restaurants and also in specialised bush-tucker menus. I have never eaten a fresh flower before but will make it my mission tomorrow to do so. I have been to several pacific islands who all have magnificent ornamental hibiscus but have never seen them on a menu over there. If is was edible I'm sure it would have been used.
