I believe there had been a large ethnically German population in America itself for some time; they're still the largest self-identified ethnic group in the country. I don't want to confuse it with "all Germans are Nazis" but I wonder if Nazi ideology itself might have appealed to some people in America with no real connection to Nazi Germany as well; I'd assume that the idea of the racial hierarchy wouldn't exclude them. Some brief googling makes it seem like American Nazi organizations were founded by recent immigrants though.
You cant look at WWII from todays race perspective in the USA and shithead nazi-american-supremacists.
It was Germany trying to conquer the Europe and rest of the world together with Japanese. Unifying their nation with hate propaganda against jews and other non-germanic people who were inferior to everyone else.
Aside from annihilation of all jews, main point was Germany uber alles, conquering all the Europe and rest of the world. Other countries conquered in Europe were countries with other white people, it was not racial in that sense.
So other immigrants living in the US would certainly not be pro-germany when it attacked UK or Poland or France or any other country they were from.
It is not something that can be applied today - as what googling around says, those nazi sympathizers were mostly recent germanic immigrants and US was always trying to disband them and lessen their influence, as early as 1933.
