Hidden on page 117 of the Apoc rulebook it is written:
"Remember that thanks to the freedom of Apocalypse battles, Chaos players can use traitor versions of any of the Imperial datasheets. For example, it is entirely appropriate to field Chaos Line Breaker squadrons, Renegade Baneblades, or Traitor Artillery Batteries."
But it need not even have been written, because there are no rules restricting the composition of your army at all. In Apocalypse your "Chaos" army can have Imperial stuff, Eldar stuff, and Necron stuff all in the same force. There are no limits on mixing different armies in Apoc.