trying to list users & display first – last name

first_name and last_name are stored in the usermeta table. Therefore you have to use get_user_meta() to return these data. Try this code snippet:

$users = get_users(array(
    // blog_id is not required and will be set by WP_User
    'role' => 'sm_flagar'
));

foreach ($users as $user) {
    $firstName = get_user_meta($user->ID, 'first_name', true);
    $lastName = get_user_meta($user->ID, 'last_name', true);

    echo '<li><a href="' . $user->user_url . '">' . $firstName . ' ' . $lastName . '</a></li>' . PHP_EOL;
}