I like the idea of a hidden "piggyback" NVR. Can you have a camera connected somehow to record both to a Bi computer and to a drive on a NVR at the same time? I can't picture how that would be set up.
For an IP camera, it's just a camera attached + video server which then connects to a network so any authorised device can connect to it and view/record the stream.
It's the same as how you could have BI recording the cameras but then also view them on TinyCam or other mobile app.
It would be different if the cameras were all connected directly to the recording device (cctv recording to dvr?) but, someone correct me if I'm wrong, these recorders can also be network connected and provide a stream to other devices on the lan.