Usually, from the cluster drop down menu in Compressor, you should see "This Computer" and any clusters that you have set up.
Check your Q-Administrator settings in System Preferences. If you're not able to submit from Compressor, try resetting Q-Administrator services from within system prefs. This often times fixes random problems with Compressor. If you have any clusters set up, resetting services will require you to setup your clusters again afterwards if you want to be able to use them in Compressor.
All the best,
"Is it me or do I spend half my life watching little grey bars turn into little blue bars??"