At the moment you need to call TWebTableControl.HideCol either after you poulate each row or after all rows are populated, otherwise rows created after the call do not hide the column. See TWebTableControl.HideCol only hides for first row - WEB / TMS WEB Core - TMS Support Center
A column property of Visible (with a default of True) would enable this to be set at design time, before, during or after row population and be respected for all rows. This would make the need to call HideCol uneccessary .