The reason you're only finding third party options is because Unity doesn't have any built in support for Bluetooth.
is there anyway Unity can support bluetooth communication between two devices?
Yes, you'll need to use a third party library to add the support, or you can write your own (not recommended).
Which library to use is up to you, find one that ...
With Unity, anything the engine itself can't do, can be done with native plugins, so I'd say you can.
However, Bluetooth is designed for master/slave personal area networks, like connecting a keyboard, or a headset to a phone. Not for high speed networking.
I guess you could use the LAP profile, but once again, it is not meant for high speed communications....