Hi Ahmed,
Flow Metadata is not only limited to RTP sessions. For example, the Webex client version FR26 supports metadata flow using MSI (medianet services interfaces). Flow metadata in this use case is announcing attributes to the network describing the characteristics of the encrypted webex flow.
Note that the actual webex session remains encrypted. Flow metadata is only being used to announce the session to the network.
In response to your second question, not all network devices along a media path must support Flow metadata. Non-medianet enable devices will transparently forward and ignore metadata signaling message like normal IP traffic.
regards,
Eric