If I may rephrase your question to "Should your car buying decision take into factor the fact that SKorea does not have as strong whistle blower protection as the U.S.?"
Car market in the U.S. is so competitive, and consumer protection so strong, that personally it wouldn't influence my car buying decision in the U.S.
If I were buying a Hyundai in Korea, then yes, it would be a factor, though how much, it's hard to say. I don't believe Hyundai would consistently misbehave like this. It's entirely possible that had the fix been cheaper for this engine recall, Hyundai may not have dragged their feet.
As to your question on Japan, I'm not really qualified to speak about whistleblower protection legal frameworks about either country. Both countries have it, but they are relatively recent concept, where there still is strong sense of company loyalty, hierarchical chain of command, saving face, and slim chance of re-employment in the same industry after whistleblowing event. It probably still needs to time to mature.
Either way, if I were buying Korean or Japanese goods in the U.S., all I would care about is product quality and performance. They are both nations of people that take strong pride (some may say too much) in their outputs, and care too much about how their countries are perceived on oversea stage that to have meaningful impact on their product quality.