Personally, the command I use is this:

  # Replace `/dev/video2` with the dummy video device added by `l4v2loopback`.
  ffmpeg -re -listen 1 -i rtmp://127.0.0.1:5050/ -c:v rawvideo -an -pix_fmt yuv420p -f v4l2 /dev/video2

After starting ffmpeg, you set up OBS to stream to a custom streaming server at`rtmp://127.0.0.1:5050` and start streaming.

It's not very efficient and there's a delay since OBS is encoding with h264 then ffmpeg is decoding that. It's not too bad for me because I can use the NVENC encoder but I'm sure there's a way to get OBS to stream raw video somehow.

I don't know exactly what you mean, but I would use something like this: https://github.com/arut/nginx-rtmp-module