In my opinion Blackzillians are a solid team. I mean, they haven't had that bad a year. Michael Johnsons is doing very well, Spong won his MMA debut and Rumble won his last fight as well.
Look at the team itself; Reem, Rashad, Spong. That is a very high level all around skillset you can learn from.
As of how much of a chance Bigfoot has, I believe he has some. Obviously, Overeem has the power advantage in both wrestling and striking. Although, he seems to fade later on. Bigfoot has a decent gas tank and some technical striking. If he can survive the first few rounds and eventually get Overeem on his back, he can win this.
That being said, the odds heavily favour Overeem.