First, it sure looks like Sourcefire's documentation has gone down-hill since Cisco bought them. I spent a couple hours today trying to find an admin guide or something for Defense Center, and I got nothing.
Still, it appears that the Defense Center can be configured to send syslog. If that's true, and you can send it to the LEM, then we could have you send in that data as a sample and send it up to our developers as a new connector request.
If I'm reading this all wrong, and the eStreamer API is the only way to pull data from the device...I'm not sure what it would take to make that work, but I will ask around.