Servo control signal as analog input
As far as i know , the accurate way of capturing such signal is to use the input capture ( Timer module ) in a microcontroller .

The reason analog read after using an RC filter wouldnot work IMO is that the Servo signal works between 0% to 10% duty cycle at 50Hz , that means even with filtering of multistage low pass filter you will have a hard time reading correct values because the resolution is low (steps)

You might also find high resolution ADC (more than 10bits) reading difficult because of noise issues.

check this figure to see what i mean filtered PWM