The VDDA in the device is not regulated. Then again there is regulation inside the analog subsystem which helps in the working components like SAR ADC, CTB. There are bias current generating circuits and bandgap references which works irrespective of the exact supply voltage. The component specs guaranteed in the datasheet are met if the supply voltages are within the mentioned limits.
Now additional to what I have said, if you are using SAR ADC with voltage reference as VDDA, the variations in VDDA will affect the result. This can be useful if you are measuring a signal which is also dependent on the VDDA supply. If the input signal is independent of the supply, it is always better to use an independent reference like Internal Vref.
So great! Thank you, Vasanth!