That's even less of a concern for the US than Brazil. Brazil was the stop over on the southern route for B-24s flying to Great Britain. It also projects more into the Atlantic make it a greater threat if U boats are based there. Argentina had even more neighbors with territorial claims I believe so encouraging and arming those countries could probably keep Argentina busy enough. The Argentine navy was pretty minimal as well. From what I was able to determine: a couple of pre WW1 battleships. A couple of "river battleships" a couple of small heavy cruisers (6 x7.5" guns) a small light cruiser (9x6" guns) and a couple of pre 1900 armored cruisers 4 pre WW1 DDs a dozen modern DDs a few smaller vessels of various vintages. See: List of ships of the Argentine Navy - Wikipedia
Neither were in the immediate pre-war and WWII era. Although Brazilian government was a dictatorship that did have some fascist overtones. OTOH, Brazil did crackdown and prosecute their home grown fascists after the attempted a coup, that failed.
Wiki had them listed as "river battleships". I thought that a rather odd term so put it in quotes especially since I wasn't familiar with the ships. Looking up the details at: ARA Libertad (1892) - Wikipedia and ARA Independencia (1891) - Wikipedia It notes:
Yes, the "Pajama Putsch" of May 1938, which led to the PURPLE exercise at the AWC Washington Barracks during the academic year 1939 that was completed in May-June 1939.
So what if the "Pajama Putsch" of May 1938 happen, could we see a period of Brazil-German relations happen until the events of the first post in this thread, maybe with Germany selling Brazil waopons.