You would have to implement IRenderLabel to get the list of items in the Others slice. You can only get the values this way, but not the individual labels.

Hashtable labelHash = new Hashtable();
labelHash.Add("CUSTOMLABEL", new LabelRenderer());
this.ultraChart1.LabelHash = labelHash;
this.ultraChart1.Tooltips.FormatString = "<CUSTOMLABEL>";

class LabelRenderer : IRenderLabel
{
   public string ToString(Hashtable context)
   {
      string label = "";
      ArrayList othersList = context["OthersList"] as ArrayList;
      if (context["ITEM_LABEL"].ToString().Equals("Others") && othersList != null)
      {
         foreach (object o in othersList)
         {
            label += o.ToString() + "\n";
         }
      }
      return label;
   }
}