Most of them only spawn once per toon, yeah. The moss covered ones are also once per toon, I think, don't quote me on that as we have not had a tuesday reset yet. Some of them are weekly though as well, I believe.
I was under the impression that the majority of chests are one time. As far as I know there are a few weekly chests but no chests that respawn on a shorter timer. The pillars platform chest, the rope bridge chest, the crane statue chest, the bag on the pirate ship in the SE corner, the chest in the under water cave off the west shore and the chest in the sunken ship to the south should all be weekly. The rest should all only be lootable only once.
I suspect that most people who claim they've looted the same chest multiple times likely looted moss covered chests in similar locations. E.g. you loot a chest under a tree with some tigers and then a few hours later find another chest under a tree with some tigers and assume it's the same one when in fact it's around the corner from the first. I believe there are 3 moss-covered chests all under trees surrounded by tigers, each one only lootable once.