If the DVR's provide a RTSP / MJPG stream then it's very possible.
When setting up BI, you create a new camera for each channel of the DVR, re-inserting the DVR's IP, username and password repeatedly for each camera but changing in BI the drop-down number for "camera"; i.e., an 8 channel DVR with 8 cameras will have 8 camera in BI, all same IP / user / pass (from DVR) BUT.....a different camera number in the drop-down menu for "Cam #."
I've streamed Zmodo and Night Owl DVR's with analog cams like that; NVR's with IP cams should also be no problem doing so.