We know that it happened, but not much about its nature or extent. Miriam Gebhardt describes one such case in Als die Soldaten kamen. A couple of others came forward in old age to PTSD researchers.

The rape of men took place in the German, U.S. and British armed forces; in concentration camps; in ghettos; and in "survival sex" situations during and after the Second World War. There's no reason to believe that it was any less prevalent in the SBZ.