Well no-one knows for sure. Different 기사 say diffeent things,which anoys me:
This one says that Omar was just a good friend of Michael and not a lovechild:
link But this one says that it has been confirmed 의해 Joe Jackson that Omar is the fourth child of Michael:
link I'm confused on the whole thing. But i agree with Joe,he looks like Jackson,acts like a Jackson and even dances like a Jackson:)