Al Hakim, the person regarded by the Druze as the manifestation of Allah, was once a caliph in the the eleventh century. He reigned not for the Sunnis, but the rival Fatimid Shia Caliphate in Egypt from 996-1021. Known as the 'Mad Caliph' for his notoriety and unpopularity, he was hated by almost everyone and hailed as a tyrant.
Christians and Jews suffered during his rule as he ordered the destruction of Churches and Synagogues throughout his domains. His most infamous action against the Christians included a partial destruction of the Church of the Holy Sepulcher, the place where Christians believe the Messiah was born. Muslims were not spared either, as he banned them from performing communal Salah according to the norms of Sunni Islam. Sunni Muslims were also banned from entering Jerusalem.
He was eventually assassinated when he ventured alone into the desert and never returned. While his killer/s was never found, no one mourned him but many were happy at his death.
As a people, the last time that I am aware of where the Druze did something for the Muslims, was in 1975-76, when they sided with Muslims against the Christians in the Lebanese Civil War.