From what I have read Germany used a good deal of “highly supervised” prison labor. Of course, some people insist that never happened. I don’t “know”.
For building bombs, and doing the dirty work probably, but in their factories that produced their planes, tanks, etc., it was all engineers...no regular laborers. It's one of the reasons it took them longer to produce them. They lagged behind the U.S. and England in production...as did Japan.
I downloaded this 8 part series from a UK torrent site last year.
It's an excellent program, and explains why the country that produces the most war machines during war time, is the country that will come out on top. One of the episodes was about Russia, and how we provided a lot of the stuff they used during the war. We sent them pre-fabbed factories, along with American engineers to help them build them, and get them operating. When Hitler invaded Russia, Stalin ordered all the factories in those areas disassembled, placed on trains, and moved further into the country to be reassembled. They unloaded the building parts onto a field, and worked from there to put it all back together again. We sent them an awful lot of locomotive engines, and rail cars, along with other stuff. Stalin halted production of all farm machinery, never thinking that people would have to eat during that time, and he never thought to produce trucks, or other types of vehicles to haul military stuff in.