It has to be an entity approved by the government for sponsoring foreign visa applications for its workers. While I don't know the particulars of the law, I'm very doubtful that an individual can do it (that's not to say that an individual with influence, for example, couldn't talk to someone at immigration and find some other way to get a person approved for residency). From what I understand, it's not an easy thing to get approved as being able to sponsor foreign workers but I don't remember if that's generally because doing many things here in Argentina related to businesses is that way and this would be more complicated than a national business, or if it was specifically that the government kept a tight control on that, or both.
Therefore, I don't see a single person, or a small corporate entity of some sort that was created for that purpose, having any chance of getting approved for such a thing. Of course, that's not counting the guy who has the right influence as well. I'd imagine anyone who is going to sponsor foreign work visas would have to show to be a going, serious concern, or have backing, business plans and what-not-else that shows a specific need to sponsor foreign worker visas as a part of the business model of a new company (like a specific requirement for skills that aren't usually found in Argentina).
As to the type of work, I'm sure it would matter to some extent (you kind of left that pretty general). For example, even though (individual) prostitution is legal here, you can't sponsor a sex worker because the only recognized legal prostitution here is defined by an interaction between two consenting adults: no other person or entity can be involved in a legal transaction, therefore it's not something you could sponsor (as much bitching as I do here at times, I do enjoy the moments when even Argentina's laws highlight the puritanism of the prigs in the US).
Even though that's true, to be more serious, it probably does have a lot to do with the type of work. Just like pretty much every country, for a work visa you usually have to demonstrate that you have unique skills, though from what I've seen over the years those rules are not greatly enforced even in the US, or at least it is easy to "lawyer" around them to create the appearance of a need. But I bet you couldn't sponsor a taxi driver, or a bus driver, etc, because those jobs belong to pretty strong unions here. I'd be surprised if it was allowed. There may be other protected industries but admittedly I don't know.
