Is it okay to use require_once for libraries which aren't CI 'compatible'?

[eluser]dallen33[/eluser]

Code:

require_once($_SERVER['DOCUMENT_ROOT'].'\directory\application\libraries\simple_html_dom.php');
require_once($_SERVER['DOCUMENT_ROOT'].'\directory\application\libraries\url_to_absolute.php');

Also, is there a better way I can write that?