The PreferredCellSize/PreferredLabelSize properties of UltraTreeLayoutInfo return 0 for the width/height components when they are not set explicitly (It think that is what you mean by "not always updated"). If you like you can visit http://devcenter.infragistics.com/Protected/RequestFeature.aspx and submit a request for resolved versions of these properties; in the meantime, the following workaround will give you the column width by finding the associated UIElements:

private int GetColumnWidth( UltraTreeNodeColumn column )
{
    UltraTree treeControl = column != null ? column.Control : null;
    UltraTreeUIElement controlElement = treeControl != null ? treeControl.UIElement : null;

    if ( controlElement != null )
    {
        UltraTreeNodeColumnHeaderUIElement headerElement =
            controlElement.GetDescendant( typeof(UltraTreeNodeColumnHeaderUIElement), column ) as
            UltraTreeNodeColumnHeaderUIElement;

        if ( headerElement != null )
            return headerElement.Rect.Width;
    }

    return 0;
}