one of the documented procedures in this installation of the ACS
ad_user_group_helper_table_name   group_type
What it does:
Returns the name of the extended attribute (a.k.a. helper) table for the specified user_group_type; if there is no helper table for the specified user_group_type, then returns the empty string.
Defined in: /web/philip/packages/acs-core/user-groups-procs.tcl

Source code:

    set helper_table_name [ad_generate_helper_table_name $group_type]

    # Query the data dictionary to make sure that the helper table
    # actually exists.
    # (We use db_quote for the sake of robustness.)
    set helper_table_exists_p [db_string "select count(*)
    from user_tables
    where table_name = '[db_quote [string toupper $helper_table_name]]'"]
    if { !$helper_table_exists_p } {
	set helper_table_name ""

    return $helper_table_name