Been there many times and this is incorrect. SP check-in/baggage drop is not controlled by DL employees. SP/TSA Pre-Check security line is controlled by a DL employee who then get sent through different paths.
I will be flying on Friday so I will make it a point to see what CP4 looks like then. I have both GE and GM status so I should get into the CP4 one way or another!
I don't use checkin/bag drop often, but I can say with certainty that this most recent Saturday, there was one agent checking credentials to enter the checkin and bag-drop area and another checking credentials at the SkyPri/PRE security line.