I was able to confirm today, after getting a longer phone cord, that the 300C's adaptive cruise option (standard on SRT-8, cheap $600 option on the C, often put on by dealer stock) DOES set off the V1 intermittently at short point-blank distances. Within one car's distance, if I point the front laser sensor at the ACC sensor, I can set it off once every 15s or so intermittently on laser. However, either increasing the distance or trying with the rear laser sensor results in no alert.
Tried also with two Whistler detectors and no alert at any distance or circumstance.
So it seems like the ACC probably doesn't operate on 905nm but is close enough that the V1 is sensitive enough to it at close distances...
And yes, the ACC is an always-on module in this car too, despite the fact that no other system in the car uses the LIDAR sensor.