Freddie, there are usb hubs. Although you can network them, I've never used one without a pc in the mix. This wiki gives a description of the hubs and states downstream devices should have access to upstream devices. This suggests it would work. I'd say the DVR's are special purpose computers, but they also seem to be pretty quirky. The powered hubs are not that expensive so it would be worth a shot. I'd like to know if it works.

http://en.wikipedia.org/wiki/USB_hub