I have seen in one of our design that +5V(VDD) and -5V(VSS) are connected to AD7226. Does it work?
My query is how does it work with -5V and +5V when the datasheet says the supply voltage should be within 11.4V to 16.5V?
The supply range in the spec table will guarantee that you will be able to achieve the specified performance.
Outside of that, there is no guarantee that the device will meet the specifications.