I am not able to generate report using TestNG+Intellij 12, also provided out path in Run configuration.
I have even updated to TestNG 6.8 by this way : https://stackoverflow.com/a/13452828/1434611
Can anyone provide some input if you are able to generate reports.
Check on Use default reporters option which will create test-output folder in your root folder with all reports.
One thing that you can consider to do is, that you check the checkbox under Listeners. This checkbox enables the automated reports. You have to change the default settings of TestNG run options to enable it for any additional runs after the first one. This solved my reporting problems.
You can add Listener like "EmailableReporter" or "FailedReporter" in the "Run Configurations",
it will generate test-output directory in your workspace.
I test it at Intellj IDEA 12.0.4