Valet mode works on the red key too
But with that being said, I LOVE valet mode in the C8. I took my wife to a nice restaurant for our anniversary last month. The only way to park was with their valet service. The valet and I talked a bit as he had a ton of questions about the car... stuff like, "how do I get out? There's no door latch." I had PIN locked the car with valet mode and when he fired it up, the look on his face was priceless. "Wow, this thing even disables the stereo?" Yep. And I told him you can't rev it and it's severely speed limited. All the windows, trunks, center console, and glove box auto locks and the infotainment screen displays, "Audio and video monitoring in progress." It's a total buzzkill for a valet
The only way to do anything with the car post PIN locking it is to unlock it with the PIN. The fob or manual key won't do anything as it's electronically bricked at that point. That being said, if I'm parking in a sketchy part of town (as in, ALL the good BBQ restaurants are in carjack central), I valet lock it before I get out. Great deterrent.