Bloodthirst skill doesn't proc "Twin Blade and Blunt" axe bleeding passive and Viper's sting set. Isn't it melee skill? Also subterranian assault (storch morph) skill can proc viper's sting set. Both skill has 7m radius but bloodthirst doesnt count as melee skill I think. Here is the video for bloodthirst.
https://www.youtube.com/watch?v=8q285im-BFc