Of course, the Criminals know this, but if they manage to stay alive after 6 mos, they're free, so it's a huge motivator.
They're sent in human waves in basically suicide missions in front of the regular forces to soften the enemy positions and if they retreat or don't advance they are killed.
And if they are successful then these murderers, rapists and robbers can terrorise the local population.
So it's win-win for the current Russian regime, at least according to their primitive barbarian mentality.