Push Notifications iOS & Android Vuforia & UrbanAirship

I have am working on a game that uses the Vuforia SDK and I want to integrate Push notifications preferably using UrbanAirship (that is what my client requested)

I have been trying to get Push Notifications to work on both iOS AND on android but have had no luck, not with UrbanAirship and not any other way, I have also tried the Pushwoosh Unity plugins.

Problem 1: Is it at all possible to integrate UrbanAirship with Unity3d? Any links/suggestions/samples would be great, I have searched but not been able to find anything relevant.

Problem 2: (if I understand correctly) is that Vurforia SDK requires the MAIN activity in the Android Manifest file, so that prevents me from implementing plugins such as Pushwoosh or other similar plugins, as to use the GCM (Google Cloud Messaging) they need the MAIN activity as well.

Problem 3: Again if I have understood correctly from all the sites/forums/posts I have read, GCM is the way to do push notifications to Android. Reading up a bit about GCM it is a general two messaging API, can it be used for push notifications when the app is not running? or am I completely on the wrong track?

I know, and apologise, for the long question, but this is the first time of tackling Push Notifications, let alone something that will work both on iOS and Android. I would really appreciate any suggestions as how to get this working. TIA!