You can disable them like this (reverse it to enable tabs):

            _ultraToolbarsManager.AutoGenerateKeyTips = false;

            foreach (RibbonTab tab in _ultraToolbarsManager.Ribbon.Tabs)
            {
                if (tab != _ultraToolbarsManager.Ribbon.SelectedTab && tab.UIElement!=null)
                {
                    tab.UIElement.Enabled = false;
                }

            }