Read this Wikipedia article and it seems that the Nazis did some seemingly pointless experiments (such as trying to change eye colour), but also some useful-sounding experiments on the prevention and treatment of hypothermia. Is any of it still used?
They were not robust, being more akin to torture than science, and they yielded no useful findings of any kind. This is all explained in detail by /u/commiespaceinvader in their answer here.
No. Please see this answer by /u/commiespaceinvader