In the sense that they're on the V-Dem index, they have election laws, they have voter rolls, they have voter turnout, etc. Yes they have one party, so you don't directly vote for the President, but neither do Americans.
Yes, the KMT dictatorship era was awful. You might be surprised to know that in Taiwan there are national holidays commemorating those persecuted by the KMT. The reason The ROC (Taiwan) is more aptly comparable to the Union when making an analogy to alternative American history is because it was the original, legitimate government of China and the PRC were the rebels, just like the USA and Confederacy.