This isn't the first time this claim has been made, but according to this site, new FBI files have been opened that pretty much confirm it. What other proof exists to show that Hitler did not, in fact, die in Germany, but lived out his life in South America
Those FBI files don't document that Hitler escaped to Argentina, they document claims that Hitler escaped to Argentina. The allies were paranoid that Hitler might have escaped so they investigated every possible lead, but there was never any concrete proof that Hitler escaped Berlin.
Let me say, in no uncertain terms, that Hitler died in Berlin, he shot himself. He did not escape to Argentina. No serious historian, to my knowledge, lends any weight to the idea that Hitler escaped Berlin and managed to avoid the some 2.5 million Soviet soldiers surrounding the city. Any article that claims that they have definitive proof that Hitler escaped, should not be taken seriously.
I might also just point out the very beginning of the documentation to which this "article" refers. The FBI gives a synopsis of the file, and it is as follows:
[Redacted] reports contact with [redacted] (phonetic). Claims to have aided six top Argentine officials in hiding ADOLPH HITLER upon his landing in Argentina. HITLER reported to be hiding out in foothills of southern Andes. Information obtained by [redacted] from [redacted] unable to be verified because of [redacted] disappearance. Attempt to locate [redacted] negative. No record of him in Police or INS files.
In other words, an informant approached the FBI and claimed Hitler was alive and well. The FBI attempted to verify the information, but was unable to do so, because the informant had disappeared, and the Bureau could not find anything about his existence in official records.
Now, the synopsis from the Awareness Time website says:
Newly declassified FBI documents prove that the government knew Hitler was alive and well, and living in the Andes Mountains long after World War II.
In fact, the primary source (the FBI report) says the exact opposite. Essentially it says that one person told the FBI that he had helped smuggle Hitler into Argentina, but the FBI could find no further evidence of this. So there's your answer, OP. The article misrepresents the primary source in order to make a sensationalist point.