Plotinus,
I’m not 100%, but near certain that tanning doesn’t run encumbrance check. If you’re tanning elk, bear skin with a bag, birchbark basket or multiple bowl: game doesn’t prompt “with the load you’re carrying your task is more difficult “ paraphrased, I’m not able to check the exact wording. Same as trapping. On the other hand timbercraft and fishing do prompt about the penalties, injuries, encumbrance, fatigue.
I don't think even the weight of the hide counts. If you look at the weight you are carrying, the weight of the hide is immediately subtracted as soon as you begin a tanning process.
True, but if you attempt say active fishing (rod) at 99Fatigue, I've had pretty abysmal success, even the fatigue gets removed with the "restful" activity the active rod fishing is. I believe they're (hideworking -- fishing) calculated differently.
IME if the game does or doesn't prompt about encumbrance/fatigue/injuries: is if the physical penalties affect the task or not.