Run ONLY Dexos spec approved oils or you could be left holding the bill if there is ever an issue! Even if your're under warranty. jus sayin-
GM isn't going to waste the 2 week time frame or money to have the oil run through analysis. Even then other oils have just as much metals, minerals, additives etc in it so there is no way to tell. Specially not on these motors. V8 corvettes that blow all the time could be a different story since it costs them a lot in repair money.