Camera Y rotation adds rotation force to player?

If you store the "forward" view orientation at the beginning with the GetTrackerOrientation() call that cyber mentioned, you can get an easy input right from the headset without needing to mess with the cameras. Checks after the center is stored would give you an angle difference, you'll just want to pull out the Y axis and multiply.

I'm guessing this approach should work, its pretty close to what you've posted, but I think working with the tracker rather than the camera angles is probably going to be easier. The other aspect here is that you can decouple the camera from the heirarchy of the whole system if you wanted and it would still work fine.

Other note, if you're going to be running this every frame, store a reference to the Transform you're going to be rotating, calling the components like that is more expensive.

public class TrackerTurn : Monobehavior {

Transform rootObjToSpin;

forwardRotationVariable = blah; //I think it returns a quaternion?
float turnSensitivityMultiplier = 1f; //Use this to multiply the rotation amount 
float turnInputVariable = 0f; //Store your input, then use it however you want

void Awake()
{
forwardRotationVariable = GetTrackerOrientation();
}

void Update()
{
currentRotationVariableLocal = GetTrackerOrientation();
float yDifference = GetGoodAngleValue(forwardRotationVariable, currentRotationVariableLocal);
turnInputVariable = yDifference * turnSensitivityMultiplier; //Clamp it to -1/1 if you want 

}

float GetGoodAngleValue(float forward, float current)
{
return compare the two, grab the y and spit that angle as a positive or negative amount back out;
}


}