It would function to hide the new category from everybody except customers you give the link to (if any). It might be overkill for this application, though - you just want the category name to not appear in the sidebox, if I understand correctly.
For that you could edit /includes/templates/your_template/sideboxes/tpl_categories.php. Find this near the top:
PHP Code:
if (zen_get_product_types_to_category($box_categories_array[$i]['path']) == 3 or ($box_categories_array[$i]['top'] != 'true' and SHOW_CATEGORIES_SUBCATEGORIES_ALWAYS != 1)) {
// skip if this is for the document box (==3)
} else {
and add
$box_categories_array[$i]['path'] == 23 or
to the if statement to get
PHP Code:
if ($box_categories_array[$i]['path'] == 23 or zen_get_product_types_to_category($box_categories_array[$i]['path']) == 3 or ($box_categories_array[$i]['top'] != 'true' and SHOW_CATEGORIES_SUBCATEGORIES_ALWAYS != 1)) {
// skip if this is for the document box (==3)
} else {
Change 23 to the cPath for your category.
This code will skip display of that category in the categories sidebox.