No, SpO2 isn't used for VO2 Max calculations. SpO2 measured at the wrist doesn't tell you anything about how much oxygen is being metabolized. Only heart rate (including HRV) and speed or power are used as input for the VO2 Max estimate. Wristwatches can't even measure SpO2 accurately when you're running around, you have to hold fairly still to get a consistent reading.