Remember that Ivan the Terrible of Treblinka, a Nazi death camp, was John Demjanjuk, who was a Ukranian.
And then there were the brutal "Trawniki Men" who were mostly Ukrainians.
From a book on the subject: "The Trawniki concentration camp in Poland was used by the SS to train more than 5,000 men in the execution of mass murder. Of these 5,000, most were eastern Europeans recruited from POW camps, including a large Ukrainian contingent. “Trawnikis” were distributed throughout the concentration camp system, with particular prominence in the extermination camps of Aktion Reinhard. Trawnikis formed the firing squads during Ghetto liquidations, operated gas chambers, and carried out various other violent tasks deemed burdensome by German planners. "