I just did a test and got it to work. Thanks to Trebor Rude for the clue.
You need to save your Camera Zoom FX photos to the same place as the default camera. You'll end up with the untouched photo as well as the photo with the applied effects in your Instant Upload on Google+.
To change where Camera Zoom FX saves its photos...
Settings | All Settings
- Change the "Camera folder:" to
Default. (It's probably on
CameraZoom.) It will now show a save location like "Folder = /storage/emulated/0/DCIM/Camera"