With some minimal testing earlier although may not be exact;
Needle Blow
1 poison damage per tick : 1 physical attack
elemental damage 1:1 (additive)
Wugong Gu
1 poison damage per tick : 1 physical attack
elemental damage 1:1 (additive)
Zhendu
No scaling at all from physical attack
1/2 poison damage per tick : 1 elemental damage (additive)
So if you compare the ratio to Lyralei’s spreadsheet,
You can see that even with an arde dagger, superior kracked shooter already outperforms viper for both needle blow and wugongu. Only for zhendu will viper perform better but that’s also the weakest and slowest DoT for wugushi.
tl;dr xbow + manamana > viper
Poison damage ticks does do 2x as well on flying monsters with 2hd bow.
Lyralei’s Spreadsheet