You can send invites between android and iOS. They are linked using the developer console (console.developers.google.com). Both the android app and the iOS app need to be in the same console project. If there is only one of each, then when sending across platforms it's unambiguous which to choose and you can just send an invite. The app invite service will send the proper short links(goo.gl/...) to install/launch the proper app per platform.
If there are multiple instances of a iOS and/or Android apps in the console project, then the client ID must be sent with the invite using Api call setOtherPlatformsTargetApplication(...) so that app invite service knows which of the console apps should be selected.
For same platform, i.e. android to android, the app selected will match the app that sent the invitation, so same platform is not ambiguous.