Hatteras has always cored the decks, but almost never cored the bottoms. I say never because at some point in the 80s they built a handful of cored convertible hulls (forgot the model, aroudn 45) and quickly stopped. supposedly, they bought back these boats to avoid any future problems.
i'm 99% sure that the 56 is solid glass hull side above WL (bottom is solid, no doubt on that)
New Brunswick era Hatteras have divinycell hull sides, above WL, never heard anything bad about these.
A call to the factory will get you an answer.