管理员添加用户后如何重定向管理员？

I have a customize admin login. I want the admin to add user and redirect to a customize page upon successful add. Is there any webhook I can use?

You can use user_register hook for this; it is called after any user is register or added to DB.

Here is the code:

add_action('user_register', 'wh_redirectAfterRegistration', 10, 1);

function wh_redirectAfterRegistration($user_id)
{
    if (empty($user_id))
        return;

    $user = wp_get_current_user();
    $curr_roles = $user->roles;
    $page_id = 70; //<-- Replace with YOUR PAGE ID

    //if logged in user is admin
    if (in_array('administrator', $curr_roles))
    {
        wp_redirect(get_permalink($page_id));
        exit();
    }
}

Code goes in function.php file of your active child theme (or theme). Or also in any plugin php files.
Code is tested and works.

Hope this helps!