The question is how is your "DGND" used, if it comes from the connector, to the ADC and then elsewhere it should be fine, as any offsets will then be referenced to the ADC, equally that divider should also connect to ground at the ADC, as a divider works both ways, it cuts down the signal, but it also allows a divided amount of ground noise to couple in to your measurement and a smaller amount to your input signal
Equally how is your power supply situation, I find it odd that this ADC does not have a PSRR specification, it may be particuarly sensitive to any power supply noise