You can add support for an app yourself! Install AutoInput (you need the beta for now, get it here), the click the + icon in the “Messaging Apps” screen. It’ll guide you through the process.
Important Note: This will only work if the app syncs its contacts with the Android Contacts app and adds an option there to directly open the app chat window for the contact
Fully tested third party apps:
Apps that work but may have minor issues: