A Mercedes technician has taken my car home overnight. I asked whether it would be safe and insured, and I was told it would be, so I was happy enough. It sounds like in the case of the OP, the dealer was telling truth, but failed to mention a key piece of information which could have avoided the issue now.
With regards to the dashcam, what would be most courteous, the dealship notifying the OP that they would disconnect the dashcam, or the OP notifying the dealership that s/he would be recording them? I personally believe that the onus should rest with the party intending to record.