The following is based on the spin off novel by Keith R. A. DeCandido and might contradict canon.
Voyskunsky was a Private in Nod's army. He spoke English, Russian, and at least one language he shared in common with his Corporal, Hugh Isembi. He joined out of hate for GDI, but couldn't stand fanatics. Thus, when Al-Rashan and the fanatic Corporal Isembi were assigned to guard Joseph Takeda, they did not get along. Isembi threatened to report Voyskunsky before learning just why he was loyal to Nod.
Voyskunsky and Isembi were assigned to ambush attacking GDI forces. They hid in a "crawl space" above a hallway that the GDI would pass through, and wore IR-diffusing suits so they wouldn't be spotted. They were armed with new Tiberium-based ray weapons, but GDI Private Ricardo Vega saw the heat of their poorly-shielded weapons due to his malfunctioning helmet. Voyskunsky was captured in the battle when Vega shot the "floor" out from under them. He was imprisoned at Fort Powell's brig.
Voyskunsky had an argument in prison with GDI Private Alessio Bowles, who had a severe hatred of Nod. Voyskunsky sounded much more like a fanatic there, and continued the argument even when Isembi started yelling at him. Eventually Isembi's responses to Bowles indicated that Isembi and Voyskunsky had reached perfect agreement. Voyskunsky and Isembi spent the rest of the war as POWs.