You could define a ValueList and set the ValueList property of the column
private void ultraGrid1_InitializeLayout(object sender, InitializeLayoutEventArgs e)
{
ValueList vl=new ValueList();
vl.ValueListItems.Add(true, "Yes");
vl.ValueListItems.Add(false, "No");
e.Layout.Bands[0].Columns["ColumnBoolean"].ValueList=vl;
}