Orcs are innocent of everything they did before while afflicted with the Blood Curse because of involuntary intoxication. Gul'dan lied to the Orcs when he gave them Mannoroth's Blood. In cases of involuntary intoxication, the person who "spiked" the drink (Gul'dan) is prosecuted for the crimes committed by the intoxicated party.
They are guilty of everything they did without the Blood Curse.