You can turn off power to PoE ports in some switches. Else I think you may run into problems as the two units are trying to negotiate who is to send power and who is to receive. If the switch has an "uplink"port, those are usally non-PoE , then you can use that port.
Come to think of it, I have successfully plugged a Xyzel PoE switch to a Cisco PoE port with not a problem.. Truth is I wasn't even thinking of the implications :)
IPVMU Certified | 08/06/15 09:34am
As long as both the switch and NVR are listed as 802.3.af compliant, there will be no power exchange between the two.
There are a few switches out there, (Ubiquiti, MicroTik), that provide "always on" passive 24 or 48v POE that you would want to avoid.
Even then I'm not sure that anything would actually happen to the NVR, as the NVR ports are most likely only using pins 1,2,3,6 for both power and data and the switches passive POE would be coming in on pins 4,5,7,8.
I'm sure I don't want to find out though.