XML-RPC function/hook for native tags

I wish to know the answer to this question as well. As I know ScribeFire is able to post to my blog with tags I would like to know how.

Can it be done? If so, how?

You can add/edit tags on a post via the mt_keywords field in the metaWeblog.newPost and metaWeblog.editPost XML-RPC methods.

function metaWeblog_newPost( $blogid, $title, $content, $tags, $category="") {
  global $g_id;
  global $g_passwd;
  global $g_blog_url;

  $client = new xmlrpc_client( "{$g_blog_url}");
  $f = new xmlrpcmsg("metaWeblog.newPost", // metaWeblog.newPost method
    array(
      new xmlrpcval("{$blogid}", "string"), // blogid.
      new xmlrpcval($g_id, "string"), // user ID.
      new xmlrpcval($g_passwd, "string"), // password
      new xmlrpcval( // body
          array(
            'title'        => new xmlrpcval($title, "base64"),
            'description'    => new xmlrpcval($content, "base64"),
            'category'    => new xmlrpcval($category, "base64"),
            'mt_keywords' => new xmlrpcval($tags, "base64")
        ), "struct"),
      new xmlrpcval(true, "boolean") // publish
    )
  );

  $f->request_charset_encoding = 'UTF-8';

  $response = $client->send($f);
  return $response;
}

I found this source code here. Works like a charm!