You could just use a standard redirect (report_start hook location):
PHP Code:
if ($vbulletin->userinfo['userid'] == x)
{
$vbulletin->url = 'index.php?' . $vbulletin->session->vars['sessionurl'];
eval(print_standard_redirect('Thank you for your report', false, true));
}
Change x to the userid of the user and then change 'Thank you for your report' to whatever redirect message you want displayed.