I've never really wanted to use the Info Share part of Carman, but it's good to know it works.
@ rotoflex: The trick I used to make it work was to pair the dongle with the N900 though it's normal bluetooth discovery/pairing system first. I then went in, connected to it (as it disconnects after pairing), and ran Carman with it already connected. After that Carman was able to see it. Since then, just connecting in Carman turns on bluetooth, finds the dongle and connects.

One note (mentioned here earlier): For some cars you have to have the car actually turned on to pair, for some you have to have it just in "accessory" mode. My smart car has an oddity that you can't clear engine statuses if the car is on, but have to pair while it is on.

Good luck!