How to print the raw value of a custom user field in comments
You can use the field_get_items() to get all values for this field, after use field_view_value().
Example below:

// user_uid_optional_load() will load the user object with all custom fields

$account = user_uid_optional_load($comment->uid);

$items = field_get_items('user', $account, 'field_name');

// as a example I'm using the number 0 as delta
$value = render(field_view_value('user', $account, 'field_name', $items[0]));