Question: Is this clock enabled in software to output the 32KHz external input or some other clock? Is the Aux Clock available in low power mode, or just active mode?
Answer: The Aux Clock is the reference clock for the PWM HW block, but it can also be brought out onto a GPIO. This clock will only be active in active mode because the output is based on the Xtal divided.
For example, take a look at the pwm_tones sample in SDK 2.0.1 as it uses the Aux Clock as an input to the PWM block to generate different frequencies. Note that IO current will be ~100uA/MHz higher when you utilize the Aux Clock.