We know that the KGB had spies and agents across the world, but did they use undercover agents to implant law enforcement specialists into criminal organizations within the USSR?
Or was organized crime not so organized back then?
What about other Socialist countries? There must've been some levels of mafia, vory v zakone, bratva, prison and gulag gangs or even political "criminals" that the law enforcement could fight better having someone on the inside. Or was government power so supreme that this was not very necessary?
If using undercover agents was never a police/local law enforcement tactic, when did it become one?
Yes they did. the ussr was probably most notorious for this, as they incorporated all the lessons learned from the previous tsarist system which heavily relied on undercover informants, spies and detectives that would root out anti-government factions or groups, sometimes labeled (sometimes accurately) terrorist groups.
Organized crime did exist, but in some places it was organized by the government. in the north caucasus, in central asia, in eastern russia, even in the 'mainstream' european socialist countries like poland, czechoslovakia, hungary, russia, and the baltic states, cross-border gun running, insurgent support, drug trade (especially in central asia) and other government unapproved activities were carried out by government agents or agencies. sometimes explicitly approved by higher powers, sometimes implicitly, sometimes not at all. think of Pakistan's ISI after 9/11. they vocally, behind president/dictator musharreff, supported the us and decried radical islamist terrorism, yet openly transported pashtun militias and pakistani fighters into afghanistan, harbored al qaeda and taliban fugitives and trained fighters in insurgency tactics, bombmaking, and terrorist methods to send into Kashmir. the same happened on the eastern side of the iron curtain.