There are a couple of potential reasons for this;


1 - There was a previous 'crash' of SteamVR and Steam has blocked etee in the 'Manage add-ons' section in SteamVR > Settings. Enable this and restart all devices and the controllers will be back.
 
2 - Check that the controllers are powered on and that the LED is showing as Purple in colour. This means that the eteeController Dongle is connected correctly. If it isn't then unplug the eteeController Dongle, wait a few seconds for the PC to register the removal then re-insert the Dongle. If they are still not registering purple then recycle the power on the controllers.