That's generous, some clergy actively participated.

Miroslav Filipović also known as "Brother Satan" was a military chaplain and Franciscan friar. He was expelled from the Franciscan order during the war for his participation, but it didn't stop him wearing the robes, which he even wore to his execution. He was the Chief Guard of Jasenovac concentration camp, the third largest in Europe, which killed up to 100k people. It was run by the Ustaše who were very involved with the Franciscans. There were forced conversions too in the camp, even if the local Bishop didn't approve and actively had participating priests arrested. Even the Nazis thought Jasenovac was too cruel.

The Pope later gave the Ustaše leader protection at the Vatican and helped him to flee to Argentina. He knew. They all knew. The Vatican was even sued in California for it and the looted gold the Ustaše took to the Vatican is probably still there too.

More info on the Catholic Church's relationship with the Ustaše