I would suggest finding the stream URL of the camera and adding those manually to the Dahua NVR.
I've done similar to get Axis cameras on my Dahua NVR.
RTSP (stream url) will have a mention to 'channel' in the string. Like "channel=0", the stream number is each camera in the unit. It's either 1 to 4 or 0 to 3.
Use our free software to connect Axis IP CCTV camera URL for RTSP streaming video. Login to Axis camera.
www.ispyconnect.com
I get rtsp:/admin_ipcamtalk:ipcamtalk_password@10.1.1.1/axis-media/media.amp with their calculator, that doesn't have anything about the stream from each camera.
I am able to access the camera settings via labtop and believe I found some setting in regards to the rtsp. But how exactly do you add that info to the nvr? I have never done that type of add.
Manual add and enter the mainstream URL and sub stream URL.
Sub stream isn't strictly needed, But when your NVR is displaying more than 4 cameras at once it needs it (viewing via the NVR's HDMI or VGA out).
It still records the mainstream without issues, but the substream is what it displays when there's many cameras decoded at once on screen.