If the idea is to use a 3rd party USB 2.0 BT dongle rather than the built-in BT hardware then the situation is no different from any other USB device not natively supported, as long as you have an appropriate userland driver library (that compiles with either SDK) to use with it, you can leverage it within an homebrew app and use the dongle for whatever purpose on HEN or CFW.
Any userland driver written for BSD or even Linux/Android might be portable as long as requirements are within specs.
The problem with this is ubiquity, each type of dongle requiring its own driver, it's a pain in the ass to release anything based on such a setup because users have to hunt for the exact type of dongles before they can use the app.
I am not aware of any "Universal" BT driver library supporting a wide range of dongles ever being either ported to or released for PS3, the only BT dongle driver library that's been used for homebrew would be the one included in the ps3xpad project to my knowledge.