There are a couple of restaurants but no true hookah lounges. I am assuming this is because they do not allow smoking indoors.
I smoked at:
Habibi: in San Telmo, they only have small table top hookahs and only two outdoor tables that will hold 3 people max. They did have a few flavors of shisha.
Al Rayon in Palermo. Very small place has about four tables outside, good sized hookah, but no choice in shisha flavor. You get what you get. But good food and great coffee.
I got fed up and just went out and bought my own pipe.