RTMP is of course not required; you could write locally to your workers, and then push to your storage repo over http, rsync, whatever. My last gig was with video broadcast, so most of my work was with rtmp, Akamai, etc. Different ways to skin the same cat. Almost all hardware video IP encoders support rtmp though, and you can colocate with where your storage is.

As /u/akiselev mentioned, SDR is easier to extend with the hobbyist community that exists around it, especially if you have a custom application and need more control.