A mail from a customer implies that it should be possible to detect other bluetooth devices without windows being paired:

Within WinRT, outside of Qt entirely, the class BluetoothLEAdvertisementWatcher
is able to detect BLE device advertising packets even if the device has not been
paired with the OS. This is the kind of behavior we are looking for.
Of course, we will also want to be able to connect to services on
the advertising BLE device and communicate with them.

https://msdn.microsoft.com/de-de/library/windows.devices.bluetooth.advertisement.bluetoothleadvertisementwatcher.aspx

This needs to be investigated and fixed if the option is indeed available.