I would be surprised if your core even needs a bluetooth dongle, unless it is operating as a hybrid or unless you are using that as the single base station for your mobile orbiter(s).
My understanding of the way Pluto wants to use bluetooth, and I could be wrong, is to have lots of different bluetooth dongles distributed as child devices for each media director. This effectively sets up a wireless bluetooth network all over the house which serves two puposes. Firstly it enables the mobile orbiters to work everywhere, but secondly (and in my view more importantly) it can pinpoint, based on single strength triangulation, where a particular bluetooth device (usually a mobile orbiter) is in the house, which then related back to where a certain person is in the house. This then enables events based on the movement of the person and things like 'follow me' to work.
I have just ordered sone USB dongles for my media directors that are supposed to have up to 160 metre range, but I would guess that the real range depends upon the device you are using and obstacles in the way.
Anyway, hope that helps a bit