No, the government of the southern half of Korea, the Republic of Korea, is not an "occupier." The democratically elected state was the People's Republic of Korea (PRK), which spanned the entire peninsula before the US Empire came in, declared it illegal, and split the country in two, against the will of Koreans, and installed the dictator Rhee Syngman in place. The PRK was a quasi-socialist state that predated both the DPRK and ROK's governments.
Again, "tankie" in practice is just a pejorative for communists, akin to "pinko" or "commie." The fact that you're getting very basic communist stances on Korea completely wrong here betrays any sense of legitimacy you have on the subject.