RTSP streams are not supported on the Xibo for Windows Player, however Xibo for Android does support RTSP. Below is a link to the Documentation for the Local Video Widget, which you would use to receive the RTSP stream:
If you plan to use the Xibo for Android Player instead for your RTSP stream, you will need a more powerful hardware solution than a Raspberry PI. I have also included a link to our Recommended Hardware Guide for the Xibo for Android Player: