For ONVIIF, the EMS does not support the "announcement" portions of the spec, but as you suggest, we can handle media streams both to and from ONVIIF systems. This can be done in a variety of ways. To initiate the connnection from the EMS you can issue API commands:
For outbound streams: pushStream uri=rtsp://Onvif/ingest/point localstreamname=theStream
For inbound streams: pullStream uri=rtsp://Onvif/stream/location localstreamname=theinboundstream
you can also both push a stream and pull a stream from EMS using an ONVIF system.
For android, we do have an EMS APK that can do stream origination and streaming.
For ios we have a developmental app that can do stream origination and talk directly to EMS on a server.