It's clear that this feature is malfunctioning with my Mercedes. If I were to bring it into a mechanic, would he/she be able to examine if it's functioning properly by using the OBD-II?

 

Is the warranty up yet? If not, drive it to your nearest dealership and have them take a look at for you...

 

they will be able to see actual values, and distance from the radar sensors.
make sure you have it turned on in the cluster. go to settings and go to radar sensors, then turn on. you have the option to turn it on or off. ive seen bad mirror glass, the blind spot light should change from red to amber on start up of the engine.