As there always has to be a first time any Argentine business hires a foreigner, I don't think a business has to pre-registered with migraciones, but they will have to take the necessary steps before that individual could begin working.
Since you used the example of working for a restaurant, it would be inteesting to know under what conditions migraciones would grant a work visa.
Perhaps, for example, the Hotel Sofitel would be able to get a "work visa" to hire a highly skilled French chef, but I have doubts that it woud be possible to secure a work visa for an invividual who does not have the level of skills that cold be performed by an Argentine citizen or somoeone who already has residency which allows them to work without getting permission (like a server or a dishwasher).