All university teaching in Argentina is based on the Soviet system- we pretend to pay you, you pretend to work. I know a few full time professors at UBA and elsewhere, they make very very little. And I know lots of professionals who teach at multiple universities- Rosario, UBA, La Plata, De Tella, and more- and they do get paid, but again, very little.
They do not have "tenure" as we know it, in argentina.
In the USA today, fully 70% of all courses at colleges and universities are taught by non-tenure track adjunct professors.
This number is going up.
But they do get paid.
Even the grad students I know get, at the very least, discounts or free tuition in exchange for teaching at the university level in the USA.
I think "unpaid" doesnt exist much in either country, but aside from the steadily declining number of tenured professors in the USA, nobody in either country makes much money teaching.
Most of the argentine professors I know also have outside jobs, often full time, in addition to teaching at one or more universities.
For instance, I have a friend who runs a full time architecture practice, and teaches at UBA all year, and also teaches periodically at La Plata, or other schools. He is the norm, not the exception.