Was Korach amongst the Erev Rav?
Korach was not part of the Erev Rav. The Erev Rav were gentiles that decided to become part of klal Yisroel when they left Egypt. Korach on the other hand was from the most prestigious families of the tribe of Levi. IN fact he was from those who had the merit to carry the holy ark. Unfortunately he made a big mistake in thinking that he can also be the Kohen Gadol.
Rashi and Ibn Ezra Shemos 12-38, Bamidbar 16-1.