I know this is a few years old, but I'm posting this because I ran into the same issue recently and was frustrated for a few days before finding the solution.
If your XML responses display correctly, but nothing shows up in the outline view, then your message structure / event handling, everything is correct. Turn on the ReadyAPI log to see if you can see any errors why the outline view didn't show anything. In my case, I saw the following message:
Fri Feb 05 11:32:05 CST 2016:WARNkipping document due to outline editor limit , size is 1433194
If this is the case, go to File->Preferences->ReadyAPI->Outline editor limit. Increase the outline editor limit based on what you see in the logs. Save and run the api test again. The outline view should now show the responses properly.