No, they haven't.

Let's look at human rights. This is Lee Han-yeol. He was killed in 1987, protesting against the South Korean government. He was shot in the head with a tear gas grenade. This LA Times article on the incident mentions...

Meanwhile, the government today released 177 people accused of political crimes.

South Korea had political prisoners in the 1980's.

This article from the New York Times talks about how these days, the police have very little power.

During Japan’s colonial rule, from 1910 to 1945, Koreans resented the police for working with the Japanese authorities. After Korea’s liberation, many officers ran the national police force, which formed the front line in suppressing pro-democracy demonstrations. After the country’s democratization in the late 1980s, the relationship between citizens and the police was upended. Fear of officers was replaced with an attitude of “citizens are your boss.” In the busy Sinchon district on a recent night, a jaywalking man blocked a police car, kicked the bumper and pulled the antenna, challenging the “jjapsae” — derogatory Korean slang for cops — to a fistfight while amused pedestrians watched. The officer urged him to go home. “We’re not asking people to fear us,” Inspector Choi said. “We’re just asking them not to abuse us.” Some South Koreans, though, accuse the police of continuing to act as a tool of the politically powerful. Kwon Kyung-woo, an online columnist and a critic of the police crackdown on drunks, many of them jobless or homeless, said it reminded him of the old military dictatorships, when disorderly citizens and petty criminals were taken to brutal re-education camps in the name of “social purification.”

I've posted a bit liberally here because I like the article. These days, if a police officer in Korea injures a citizen, they are civilly liable. It doesn't matter if the citizen was committing a crime. This stems from the 1970's and '80s, when the police would arrest and torture people whose only crime was dissent. When the Sixth Republic started in 1987, the laws governing the police were changed, restricting them very much.

In the 1970's, there were 8 men summarily executed after show trials on charges of treason and violating the National Security Law. In fact, the KCIA created the political party that these people "belonged" to. In 1973, Kim Dae-jung was kidnapped and almost murdered by the KCIA on Park Chung-hee's orders. This interview with Donald Gregg, the CIA station chief in 1973 who worked with Philip Habib (for whom the US Ambassador's residence in Korea is named) and who himself was the ambassador from 1989-1993 is fantastic. Very eye opening into the intricate dance that spycraft and diplomacy take, especially in Korea.

In 1960, under Syngman Rhee, a student protester was killed and found in Masan Harbor which touched off even MORE rioting, leading to Rhee's ouster, an ineffective government for a year and then Park Chung-hee's coup. During the April 1960 protests, government soldiers shot protesting students with exploding bullets.

So, the North and South Korean governments have shared a common history of abusing their people's human and civil rights. Clearly, after 1987, things become much better in South Korea - Chun and Roh Tae-woo were tried, convicted, and sentenced to death. They were then pardoned by Kim Young-sam with Kim Dae-jung's blessing, a man who himself was sentenced to death by these same guys in the 70's.

Now, I've only addressed the human/civil rights issues. Kim Il-sung/Kim Jong-il were dictators - okay, we can probably all agree on that. Park Chung-hee was a dictator. Well, you'll run into a bit of a problem here. He DID resign from the military and run for election as a civilian. He did have competition, which he handily defeated because under him and the National Council for Reconstruction, things WERE getting better. I'd be hard pressed to say "Park Chung-hee circa 1965 was a dictator." Now, "Park Chung-hee circa 1975 was a dictator" is a lot easier to get behind. Park dissolved the government, had a new constitution written that was approved with over 90% support, and he gave himself some pretty serious powers. But honestly, unless you're asking a parliamentary question, I think these issues are small potatoes compared to the actual effects I've mentioned above.

TLDR - No, they haven't.