Various talents and traits do not proc off the stormfiend packmaster/rear headshot.
Waste Not, Want Not, Makin’ it look easy and Thrill of the Hunt do not proc
Burst of Enthusiasm does proc
Exuberance does not proc
Drakira’s Alacrity and Piercing Shot do not proc
Double Shotted does not proc
Inspirational Shot and Conservative Shooter do not proc
Headshot/Crit melee THP does proc
However, some of these can proc on the back/around the belt of the stormfiend.
-Exuberance, Drakira’s Alacrity, Piercing Shot and Double Shotted.