I have checked TransmissionBT, uTorrent, qBittorrent and Deluge. Some of them offer RSS support, Deluge has a plugin, but none of them seem to offer it via the web interface. I have a headless server so I absolutely need this to be in the web interface.
A potential option is if the daemon accepts GUI connections from a desktop that will allow me to configure RSS which will then run headless once I disconnect. I think Deluge could do remote GUI connections IIRC?
This is for Linux (Ubuntu Server 16.04 LTS).