The Thing
They have announced that the most important aspect is to make sure the character is portrayed by a Jewish actor, because that is essential to the character, regardless of Race, Creed, Color or Sex.
I've been reading comics since I was a kid. I have only seen one single reference to Ben being Jewish. And that was in a Marvel handbook. I have never once seen him referred to as Jewish in the stories (It is very possible I just didn't see those issues). If anything, I was always under the impression that the Yancy Streeters, his former gang, were an Irish street gang.