PHP configuration via php_flag or php_value in .htaccess only works when using mod_php, not PHP-CGI, which is the default at Dreamhost. You may be able to make your changes using ini_set().
Since you're just dumping the URI path into an array, you can change $SERVER['PATHINFO'] to $SERVER['REQUESTURI']. Using your example, 137 will be found in $pathdata.
This has nothing to do with symlinks or mod_rewrite (which, to the best of my knowledge, is enabled by default on all DH shared servers).
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