You can use OBS with the OBS-gstreamer plugin. Gstreamer will happily receive a stream from an IP camera, but you can also connect an extra USB camera to the Raspberry Pi companion computer in the ROV, and set up another video stream through the start_video.sh script.
Note that if you’re using a USB camera you’ll want something like the bluerobotics low light camera, both for its low-light performance and because it encodes to h264 on the camera itself, which means the raspberry pi just sends on an efficient stream over the tether connection, instead of having to first encode the frames in a streaming format.