AREF Voltage same as VDD but through a reference IC
There is usually a 0.2V margin for CMOS inputs outside the rails and a low current limit for Precision voltage references.  But in your case only 0.1V for ADC input.

https://www.digikey.com/product-detail/en/texas-instruments/LM4128BMF-3-3-NOPB/LM4128BMF-3-3-NOPBTR-ND/1284497

0.1% 20mA. 3.3V. $1 (1 pc)

Further protection could be done with enable output parts and low Vdd  detect circuits, if you are unsure or check load current and add RC additional current limits/ filter to Vref to reduce to 5mA.


  You could also consider 3.0V Vref regulator and Sch. Diode clamp to 3.3V. or better yet use a 16 bit ADC with an internal Vref.