Did you switch to the proxy account before using rtmpsuck?
Did you remember to make the directory it is saving to shared across both user accounts, yours and the proxy?
Are you sure its a rtmp/rtmpe stream?
It could be regular http flv/f4v stream and in that case the firefox addon
DownloadHelper would be all thats needed.
If it is rtmp check the syntax used for the rule monitoring, remember to include "\!" without the quotes.
If you did all that and no stream try other rtmp sites see if theres no downloading what happens when you invoke rtmpsrv?
Does anything display?