That's right. They got wiped out at Stalingrad ( I think ). The few survivors were given a choice. Take a one way ticket to Siberia or join a "Yugoslav unit" ( I can't recall the exact name of the unit. John Ericksons' book on the Eastern front details it ) and fight with the Soviets.
I found the relevant paragraph.
It talks of Djilas visiting the Soviet Union in 44, and finding out that the Yugoslav Anti Fascist Brigade was made up of Croats who'd been sent to the eastern front by Pavelic, captured with their commander, Mesic, at Stalingrad, and "re educated". The Anti Fascist Brigade was officered by Soviets and with a smattering of Yugoslav communists who'd somehow survived the purges in the 30's who acted a political commissar