Yes, with a few caveats. In-app messages can be sent to your entire app audience, not just those that opted-in to push notifications. Caveats:
- iOS7 users can only receive in-app messages if they are opted in to receive push messages.
- iOS8 users will receive in-app messages even if opted out of push, except if they have disabled the Background App Refresh feature.
- As a developer, you can allow your users to disable in-app messages if you would like to give users the choice.