The rumors claim that he is. Michael's father said that he is his son but I'we never heard Michael admiting it. In my opinion , there are chances that he is because he looks & behaves like that way but we'll never know.
It's a rumor. Omer isn't Michael's son. And like it was said, I'm sure Michael would have said he had a 4th son and Prince and Paris, along with Blanket later on, would have known if he was their brother.