I think it depends on the definition of "concentration camp". The Reich used the term Stalag (POW camps for enlisted men), Oflag (POW camps for officers), Stalag Luft (POW camps for aviators), Marlag (for naval personnel), Milag (merchant marine personnel), and KZ (Konzentrationlager for non-military).
The term KZ actually was the German translation of the English term Concentration Camp, developed by the British to describe their prisons for enemy Boer during the Boer wars. I think generally today the term "Concentration Camp" usually refers to the horror of the Reich death camps.
Regardless of all the above, W/C Rees was a hero.
Tom