You mentioned you ran the SQL in the customer database, but did you also run the SQL for the configuration database? This is the SQL that creates the ability to enable/disable the checkbox through the administration panel. Also without this SQL change the code in create_account.php will not recognize that the feature is enabled and will not show up. This is likely the problem.
The sql you need to run is:
INSERT INTO configuration (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added) VALUES ('Agreement', 'ACCOUNT_AGREEMENT_REQUIRED', 'true', 'Display agreement checkbox during account creation', '5', '7', 'tep_cfg_select_option(array(\'true\', \'false\'), ', now());
Hope this helps.