It's pretty obvious that Zygarde is the third member of the eco trio.
So yes, it does get the same battle theme as Xerneas and Yvetal.
Also, Battle! "(Successor Korrina)" (the official name of that song) is my favorite battle theme of that game.
I've heard of Yveltal, but never of Yvetal.
I kinda like the Elite Four theme the most of those songs. ^_^
SHANE: You're not the only one. I think that the Champion's theme borrows from the XYZ theme.