In every concept of him, he's always been referred to as Ghoulbark (which is more memorable than his first name anyway).

Is he an undead treefolk?

He's a sickly human plant-based druid that bound a parasitic vine to him as life support. Unfortunately not as cool as an undead treefolk. Despite the background and name he only uses green magic. This representation of him only shows the most basic of his druidic capabilities. Ghoulbark came to Okundwa to study the flora and see if he can find any plants that may help to prolong his life. He has an interest in the magic of the revered witch doctors of the plane, but is hesitant to learn it himself since most of it is drawn from the dead (almost entirely humanoids and animals) rather than living plants. Presently, he is trying to make healing hexes by channeling the lifeforce and nutrients of plants onto others. Though moderately successful, his style is (at least presently) still not as powerful as the standard fetish-based magic that's so common in Okundwa.