The Cellphone input is for OnStar. Onstar operation sends class II data to the head unit to mute the other audio and activate the port. It's not something one would just connect.
Bluetooth adapters use other audio connections and control those for it's operation.
The radio mute would best be connected by how the adapter describes it's connection to it. If that is not covered in the instructions, It would be better to contact the adapter's tech support or Jason/JP Customs.
Line-out would not be "automatic" unless an accessory device (such as XM/EXternal CD or RSE were active) Then the aux in would be selected and port the audio. Unless they send class II data to the radio to select an aux device, you would need to do that manually.
When BT is active, will your phone still ring locally? If not, the port would need to be "ready" for incoming audio.
If the adapter routes that to it's own speaker, then you won't miss that. Then you may need to select your truck's audio manually to proceed with audio through your truck's entertainment system.
I would consult with Jason (JP) to better understand the details of his product.
Good luck!
