Currently I believe all necromancer pets have the same lifetap graphic, the vanilla level 1 Lifetap spell graphic effect.
This was only true for the 44th level pet, Cackling Bones.
The 49th and above Necro pets should have a spinning skull lifetap proc exactly like in this video with the spectre:
https://youtu.be/pMiyJR_iTvY?t=49