I get the impression DW didn't like or trust Chad, and kind of made that clear . But he knew MG was being influenced by him...at least through Lori. So if I were in those shoes, I'd tiptoe around it too, and not want to upset my girlfriend by creating a scene in my hostesses home.
I personally believe in and have experienced intuition in sensitive people. I've met people who I found creepy and it turned out later to be matched by their actions. Others have talked about this, that the first time they met someone, the hair stood up on the back of their head...and that person was a murderer. Chad's sister in-law Heather, talks in interviews on youtube, about how she never trusted him, she had a very bad feeling, but she didn't know why.
I don't believe MG was in on any conspiracy, otherwise in the phone call she recorded, Chad and Lori would not have said they knew where JJ was, but it wasn't safe to tell MG. They would have said 'hey, you know where JJ is, why are you acting dumb?
JMO