As all information down here I am not sure on this one but I was told as an American for example you could go to Uruguay on a DNI because a visa is not required for an American to enter URU. Brazil on the other hand requires a passport as a visa is required. This information was obtained at the airport in Buenos Aires on the way to URU. I was just curious as I had a passport too. But we all know how information works down here.
Maybe someone can verfiy this but I do not think I would buy a flight or something unless I knew for sure a DNI would work.