Visible crew/equipment: Towards the end of the film, as Snyder hustles Lonnegan out of the room (Spoiler alert!), believing that Hooker and Gondorf have been killed, an extra in a pale grey suit with a red tie stands with his hands up. The shadow of a Sennheiser microphone shows up clear as day on his costume.
Visible crew/equipment: When Robert Redford is being chased by Lt. Snyder, he jumps from a high place to the ground. One can easily tell it's not Redford but a stunt double.
Chosen answer: Snyder only knew that Erie was friends with Hooker, and he wasn't on Lonnegan's payroll, just a run-of-the-mill corrupt policeman, so he didn't know Erie was involved. The Courier barely saw Erie and so may not have been able to identify him as well as he did Hooker and Luther, so Erie was unknown to Lonnegan.