Most NVRs will provide basic support for any camera that supports ONVIF. Dahua/Hikvision cameras have a better level of motion detection (Dahua calls theirs IVS, Hik calls theirs Smart Events) built into most of they cameras, and that only works if the NVR and camera brand match.
So you could add a Hikvision camera to your Dahua NVR and it would record/etc, you just couldn't use the cameras Smart Events feature. That would limit you to using the camera's basic version of motion detection which is a pretty big step-down in motion detection capabilities, IMO. Most of the newer Hik/Dahua camera models are starting to add better filters into their IVS/Smart Events (i.e. only trigger if a person and/or vehicle is detected), so not being able to utilize those because your NVR brand doesn't match the camera might be something to pay attention to.
Note all of the stuff above would apply if you had a Hikvision NVR and were thinking about adding a Dahua camera to it... just wanted to be clear that you didn't buy a bad NVR model, it's just how NVRs in general work.
