Yes! Is does.
Flac files are supported by Nero 9. Here some information that will help you:
1) Flac files are supported when creating "Audio CDs" and not when creating a "Jukebox disc". When creating Jukebox disc, you can only use WMA, MP3, or Nero Digital Audio files.
2) You should be able to add flac files to a "Nero Express"/"Nero Burning ROM" - "Audio CD Compilation". If you receive an error message that you need a plugin, it is because this specific flac file is not supported by Nero 9. You don´t need a plugin in this case, and the message displayed is wrong. This will be fixed in one of our next updates. In this case, the problem is probably related to the flac files having ID3 tags before the flac identification. This is not allowed by the standard, so in this case the file will not recognize it as flac file by Nero. We are already working on a solution to this problem that will be implemented in one of our future updates.
I could reproduce this problem here, but as I said before, only with flac files having ID3 tags before the flac identification.
3) If this is not your case, then I please contact Nero TechSupport and send them a test file to reproduce the problem.
Hope this info helps!