First Treasure hound did not stack with native TH ability
Then SE "fixed" it a couple of years ago to stack with native TH ability.
Either SE did not fix it or they have messed it up since (or im doing something wrong).
cause I'm not receiving the th +1 effect
[10:50:51] === Area: Valley of Sorrows ===
[10:50:57] This area is currently affected by the Super Kupower: Martial Master!
[10:50:57] This area is currently affected by the Super Kupower: Blood of the Vampyr!
[10:50:57] This area is currently affected by the Super Kupower: Treasure Hound!
first upgrade proc on ademantoise gave me this:
[10:59:34] Additional effect: Treasure Hunter effectiveness against the Adamantoise increases to 8.
im in full th7 gear (knife +2 relic hands and +2 emp feet)
Also side note it seems you can proc upgrade on your first hit.
I don't have the log of this anymore but i got th8 proc on my first hit on adamantoise once