RTSP sets up two RTP channels which transport the actual audio and video data. UDP is often used as the transport protocol for that UDP. To force the use of TCP, both the camera and the EMS have to agree (and support) the use of TCP. You can set the forceTCP=1 parameter in your EMS pullstream command to coerce the RTP to use TCP.
The EMS does support the use of an RTSP HTTP proxy. The format of the pullstream is as follows: