I want to like Derrick because he is playing, what many I've talked to consider, to be in the top 10 games of all time. He is controlling everything and has no blood on his hands. But I agree with your points. In theory, the houseguests could compare notes at some point, his game could unravel, and he ends up with 7th place. There is still a long way to go.
Does anyone think that he might lose his job after this? I mean, he is on a show with 9 million viewers who now know what the undercover cop looks like. And who thinks that Zach will ever even get a job after this? He is unemployed, and you know how employers now a days do such intensive background checks before hiring...