Although we leverage the Bluetooth radio during the setup process, we do not yet support Bluetooth at the user firmware layer via the Particle Device OS for the nRF52840. This is a high priority feature after we solve the initial mesh stability issues, and is likely why you’re having issues compiling the Adafruit Bluetooth library for your Boron.
Are these the only errors that get reported?
If so, you could try a local copy of the Adafruit_BLE library which you can then namespace to not conflict with other definitions of err_t which is widely used in the Particle firmware repo for multiple purposes (also namespaced).
But since @rickkas7 is the contributor of this library, he might find a more sustainable way to leverage this issue (filed on GitHub)
Not yet, at least using the Boron’s BLE radio. Until the BLE API is implemented, you would have to use an external BLE radio. As Will said, it is a high priority project for our engineering team to get the API up and running.