feeding scaled down voltage to XADC (Xilinx)
Regardless of the circuitry or the choice of an ADC, at the end of the day you will be left with an integer digital value from the ADC.

You are responsible for understanding how that integer corresponds to the voltage at the input. Then you have to design your feedback algorithms taking the conversion factor into account.

If you are worried about the stability of your feedback algorithm then you should be looking at the resolution, linearity, and accuracy of whatever ADC you use.