With Flash RTMP there is a NetConnection and a NetStream, represented server-side by IClient and IMediaStream objects. Flash can connect to Wowza and you can do many things server-side in onConnect like validation and the 302 redirect method where the connection is rejected (used in the Load Balancer). You can't do any of that where connecting and streaming are the same thing, and because there isn't a two way communication you with HTTP and RTSP sessions.
You can see what methods are available in the Server-side API or using code-hinting in the IDE. Or you might look into the StreamNameAlias system:
How to get the StreamNameAlias AddOn
This is one of the examples in package readme:
Examples stream alias file 1:
# Fork streams off to multiple origins