I was quite confident that they were either objects or npcs, It would be convenient if they were npc as it would be simpler to make them follow you. However have you tried looking either on npc/object lists for the chair? rather than trying to figure what it is inside your server?
EDIT: didnt realize this was so dead the post was back from march jeeeeeeeeeeeeeesus what happened here.
That picture is actually from old school runescape using one of the available custom clients.
I've also tried looking through every single npc list and object list for any chairs bearing any resemblance to this one, but there is none. However I was able to use another OSRS client called TRiBot that actually detected and displayed an id for the chair. Turns out it is an NPC, but with a null id of 3567. Spawning this id spawns an invisible npc, and turning into the npc id also makes you invisible. I'm thinking there's something needed in order for the npc to become visible, or it could just be a different id.
Also I'm wondering how other 317 servers add these moving draynor chairs into their servers? Any help is appreciated!