Sun Yat-Sen was basically a socialist, and had strong communist sympathies, though he was not completely on board with it. The KMT was a broad coalition of interests in Chinese society that sought to have China rise up and overcome western imperialism. It included the capitalist and feudal landlord classes, who had an interest in seeing China become a great and wealthy power and defeating imperialism, but not necessarily in disrupting the traditional hierarchies of Chinese society too much. This is why that class sat in an uneasy coalition with the Communist party and later sought to have it destroyed after Sun died and Chiang Kai-Shek took over. However, every constituency in the KMT knew that they needed to use state power and economic planning to raise China out of poverty and resist Western imperialism- methods that might be considered socialist.

My impression was that the KMT were essentially like the nationalist in German, Japan, or modern USA (they very well may have been, I suppose).

So, yes, they were nationalists, but there's a big difference between how nationalism functions in Imperialist countries verses how it functions in countries that have been exploited and colonized- in the latter case, nationalism can be a potent force for liberation. In that sense, Sun Yat-Sen and even Chiang Kai-Shek are more comparable to figures like Gemal Abdel Nasser, or Juan Peron than they are to Hitler. They were nationalists trying to overcome the contradictions of a country that had been exploited by imperialism, and they saw the necessity of socialistic methods to accomplish this. This is because economic nationalism doesn't put profits at the center of a country's economy, and a colonized country doesn't have the option of generating superprofits at the expense of a colony.

And I'm including Chiang in this category, despite the fact that he was a monstrous anti-communist fanatic, initially feckless in the face of Japanese invasion, and wound up being an imperialist puppet who was totally reliant on American support. When he actually had the opportunity to see his vision of nation-building fully carried out in Taiwan, he didn't just allow the Chinese capitalist class to pursue profits at the expense of the nation, but rather utilized their position to generate wealth for Taiwan, and undertook a very effective land reform program.