What I have seen done in the past, and assisted in installation, is a camera that feeds it's signal back to the machine room via twisted pair or coax (whatever is available in the traveling cable). Then, the camera's feed is installed into a device that converts the signal to a digital feed that can be piped into the building's LAN backbone to whatever location is desired.

Unfortunately, at least in my jurisdiction, I have yet to come across a traveling cable that contains the necessary CAT5 wiring to facilitate this.