Labor aristocracy are proletariat still, just ones that are paid just well enough to have their interests (generally) align with the capitalists. For example, people who identify as “middle class” are labor aristocracy.

To learn more, I’d start with the source: Lenin’s Imperialism: The Highest Stage of Capitalism. In this original context it’s used to explain how companies use superprofits extracted from exploited colonies to pay off the working class in the developed world enough to blunt class consciousness at home and suppress solidarity for workers abroad.