What was Hitler's plan for foreign nationals of countries not in war against Germany (including the US before entering the war) and living there during the III Reich?
You are asking several questions in your post and the subject line which have to be answered separately:
- What was the plan for foreigners?
- What actually happened to them?
- Did it matter if they were from friendly, hostile, or neutral countries?
As it happened, some so-called 'germanic' nations fought against Germany and were occupied (Netherlands, Belgium, Norway) while so-called 'lesser' nations allied with Germany (Spain, Italy, Japan, Romania, Bulgaria, ...). People from occupied countries also had to make their individual choice to collaborate or resist.
Desperate for manpower, the Nazis actively tried to recruit helpers in the east, despite the fact that these were from 'lesser' races according to the Nazi worldview. They despised these men, but they used them. One cannot know what their fate would have been in case of a Nazi victory, a cruel death or a somewhat honored position?
By comparison, Dutch citizens could get German cizitenship (and a conscription notice) if they lived in Germany. The same applied to Polish and other citizens of German ancestry after the occupation.
There were even a few veterans of the African colonial auxiliary forces in Germany, the Nazis really didn't know what to make of them. Celebrity or dangerous precedent?