Can an ADC be damaged by applying a higher voltage than VREF but that is still within specs?
That would be written in the datasheet.

If the absolute max rating that applies for the input pins is given as "5.5V", you're fine. If it is given as something like "VDD + 0.5V", you're not fine.

Every bit of information and the way it is written makes sense in a datasheet. Always.1



1. Unless there is a mistake in it. Which happens, too... And when it does, that sucks.