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
Check on Use default reporters option which will create test-output folder in your root folder with all reports.
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
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.
From Edit Configurations