After updating OS version from 10.0.9.388 to 10.0.10.263, our GCM implementation started working (advice by people from Blackberry Support team).
We got the registration id after calling GCMRegistrar.register and now we are getting notifications! So there is no need to use Blackberry SDK or any other third party library.
If you are porting your android app to blackberry, make sure your android.cfg is well formed and with valid data received from Blackberry mail after registration for push services. Also check if push notification permission are in the manifest file in your repackaged .bar file.