Yes, it supports bluetooth stereo audio. You'll need to make sure that your bluetooth headset is paired as a stereo audo device vs just a headset (should have a little icon of a headset next to it after pairing). I've streamed audio from captivate to my car stereo over bluetooth no problem.
In the standard music player while playing a song you should be able to hit the menu key and select an option "via Bluetooth". Assumes you have a streaming capable headset paired with your phone.