using vampire feed on an NPC? I'm aware that other NPC's can see what is happening. But I'm not sure that other players can also see it. Mainly because I've never seen it happen. And unlike a player stabbing an NPC, a vampire could be some distance away. This question also stands in the case of an assassin throwing 'The Blade of Woe'. I've done both but never have I seen anyone else do it?
in that case im pretty sure its possible to see another player do that, since you can see other players use the blade of woe
at the same time though, its easy to break the animation of that at the same time (the person doing the blade of woe or feed can interact with the dead npc early to kind of animation cancel the rest of it)
yes, you can definitely see other players use blade of woe or vampire feed on an NPC
the animation is short though so very easy to miss, and for me personally i usually only hit the NPCs that are extremely isolated, as in theres not even other players nearby
as for the animation canceling, if you blade of woe or vampire feed an enemy and they have a lootable corpse, if you loot the body while still in the animation it will cancel the rest of the animation (allowing you to move sooner after using the blade of woe or vamp feed instead of being locked into the animation)