Even though in game in the unlearned tootip it says Decay Chests it does drop from the Bracken Hide Dungeon any instance, mobs or bosses in the dungeon and open world BH plus the decayed chests.
Personally much easier and less stress/disappointment is to clear m+0 for the week and just craft there. Only inconvienance is having to fly there and the still run all the way from the beginning of the instance to the alter.
What could be a a very nice QoL change from the devs would be that when standing at the alter you should be able to see and advertise in trade chat. We can only hope they might still add this at some point in the future. My leatherworker thanks you in advance!