It might depend a bit on the nature of the occupation - During Untermehnen Rettung (the huge evacuation from Prussia and the Baltic states), Denmark received a bunch of German refugees and wounded soldiers, and their hospitals were under instruction to only receive them if it was a life-threatening condition, and that the German military hospitals should take care of them otherwise (at least according to The Naval War in the Baltic, but it was written by a Dane so I expect the Danish stuff to be accurate). It might also be the case that hospitals in occupied countries may be less likely to "go the extra mile" or to have the same access to equipment and medicines. I'm not sure it's something that would be worth modelling in-game though.