One of the purposes for splitting the planes is to force you to be sure that the return currents for the analog and digital run in different sections of the ground plane. If you ever have a signal that crosses the split you have definitely caused some serious problems.

If you are not careful, a split ground plane could cause more problems than it solves. Both grounds also are connected together at the ADC or DAC and also probably at the power supply. So there is the possibility of a ground loop.

My recommendation is to layout the PCB with a split ground plane. Route all the digital signals on one side and all the analog signals on the other side. Then when you are finished you remove the split and have one solid ground plane.