My Argentine friend shocked me a couple years ago when she told me there are many openly Nazi people in Argentina. She said there are even some in her church (it is a German speaking church, not sure which one). But I have read that the CIA helped to relocate 10,000 Nazi war criminals to Argentina as the war began to go against Germany. Is that true? I don't know but there are stories of Mengela going to Brazil and experimenting with pregnant women there--and so on. Another aged Argentina woman has told me about people she knew in Patagonia who saw German subs come up close to shore and people splashing in to shore. Interesting subject. And this story just adds to it.
I don't know if you can say that about the CIA, although they were involved in protecting a few "assets" in South America in the early Cold War, such as later convicted war criminal Klaus Barbie who relocated to Bolivia.
Most of the hundreds and possibly thousands of ex-Nazis that fled to Argentina instead made their own way or were smuggled out of Europe via support channels through the Vatican. As such, most were Catholic. While most were involved in the Third Reich effort and Nazi members or sympathizers, many wouldn't likely have been convicted as serious war criminals by the Western Allies.
That being said, Argentina was the home of some of the most notorious Nazi war criminals, and some of the worst perpetrators of the Holocaust. The most notable of course was Adolf Eichmann, manager of the bureaucratic machinery that ran the Holocaust, who had faded into obscurity as a foreman at he Mercedes-Benz factory and living in a house on Garibaldi Street in La Boca when he was captured by Israeli Mossad and spirited out of the country to be tried in Israel - unrepentent of his atrocities.
Others later convicted of war crimes after residing in Argentina included Erich Priebke, leader of the Ardeantine Caves massacre. Among those that lived in Argentina but weren't convicted included Josef Mengele for a time (died in Brazil) and Eduard Roschmann (died before extradition). It is generally accepted that the government of Juan Peron was aware and accepting of their prescence. Similar sanctuaries existed in Chile, Brazil, Paraguay and other South American countries.
Honestly not sure about the U-Boats, but not implausible. Famously, the German battleship and raider Admiral Graf Spee was sunk in the Rio de la Plata by the British Navy in the first months of the war. I believe some of the crew are buried in Buenos Aires.
