Pets count as mobs. As such bramble will work on players provided they are within it's effect range. Players hitting from long range (+range weapons) might avoid it.This isn't location dependant. Pet bramble works in TW, open world PK and any instance.
You need to be in range of the pet, not the veno. Also, was the pet fighting back? It's reflect does not work unless the pet is attacking the target.
This PW ... so many weird things. I did stand in the mob attacking it, but the mob didnt fight back.
BLEED. That is all.