It has just leaked 22 Chili Peppers demo songs, including never-before-released and unfinished ones,...
Yes, it is correctly used. Used in the normal subject or object position when a more specific subject or object is given later in the sentence.
according to OxfordDictionaries.com
Plus, in English we try to have a subject in a sentence. Sentences without a subject only in rare cases, so "it" works as the subject in the given excerpt.
In Portuguese we can translate "without a subject" (vazou...veio ao conhecimento público, foi divulgado [sem citar a fonte], 'saiu" na imprensa, nos jornais...etc).