All that "traditional druid" stuff is a romantic fantasy invented in the 18th century, and considerably embroidered upon more recently. The Roman reference to "Wicker Men" -though genuine- is a single one and we don't know if it's in any way accurate. Beware of attaching significance to such things. It's likely that the Klan bought into the fantasy, of course; I know very little about them, but I do recall that they used to give their officials fanciful "cod-druid" titles like "Grand Dragon" and so on. The hoods are not druidic. They appear to derive from the Inquisition and the Auto-da-Fé. Perhaps someone could give specifics on that.