I'm pretty close on this one. I took advantage of the EnableEmptyListItem to add an string telling the user to select an item. I have a CompareValidator that is picking up the empty list item text. What I would really like is to pick up the empty list item value, which is zero by default. Here's what I have and it works on the text in the radcombobox.
Here, the emptylistitem text is "Select a category". I can live with this, but if it's possible to get the value field for the comboboxcontrol, that would be great. Thanks.
GridDropDownListColumnEditor category = (GridDropDownListColumnEditor)item.EditManager.GetColumnEditor("RiskCategory");
TableCell catcell = (TableCell)category.ComboBoxControl.Parent;
CompareValidator comp = new CompareValidator();
comp.ID = "compID";
comp.ControlToValidate = category.ComboBoxControl.ID;
comp.ValueToCompare = "Select a category";
comp.Operator = ValidationCompareOperator.NotEqual;
comp.ErrorMessage = "Please select a valid category";