If your router is anywhere vcose to being set up typically, the router is assigning numbers like 192.168.1.x or 192.168.0.x to everything connected to it, right?
The NVR will be talking internally to cameras with completely different numbers, say 123.321.1.x where X is the individual camera's number. The router will never assign a device a number through DHCP that isn't 192.168.1.x. Your NVR will be assigned an address like 192.168.1.9 so that other devices can talk to it through the router but the NVR basically does the talking to the cameras on the NVR's own set of numbers which are assigned internally by the NVR to the cameras. Nothing that is assigned by the router should ever conflict with a number assigned by the NVR to its own cameras, although an IP address conflict may knock out the entire the NVR from the network if the NVR gets conflicting numbers from the router with something else, say two things share 192.168.1.9 by accident somehow. The NVR will still be recording the cameras just fine internally, but nothing will be able to access the NVR from outside the NVR.