There's a tiny bug with the alt avatar for Defiler. Apparently when you cast her ulti there seems to be no souls coming out or visible. My friends were asking the same question and realised that they couldn't see the souls when I casted the ulti for the alt avatar for Defiler.
Jungling and Support = Best Roles Ever!
Confirmed, but it's only a visual effect: in fact when you attack someone or something with ulti you see the souls on it, and the damage too is applied.