I want to trade some Pokemon from my Pokemon Y game to my new Omega Ruby game. I've nicknamed all of them, but I've heard that if they evolve after being traded their nicknames revert into their species name. Is this true? And if so, is there any way I can bypass this (like using the Pokemon Bank)?
Yes, when they evolve they do change back to species name.
Example: Let's say you have an Oshawott named Ottaro (Oshawott's German name) in your English language game. When your Oshawott evolves, the name will go back to Dewott [In English].
Source: Experience-and this http://bulbapedia.bulbagarden.net/wiki/Nickname