Can I Use TestFlight Beta Testing for Apps Not Created Using Xcode?
No, is not necessary. You can upload your app from both Xcode or Application Loader.


  Application Loader is a tool to help you upload your apps to iTunes
  Connect. It’s particularly helpful if your app includes In-App
  Purchase products that need to be configured for the app. Application
  Loader is explained in Using Application Loader. Application Loader is
  available from the Resources and Help section of iTunes Connect.


With that tool you will be able to upload your .ipa file. Once your app is upload, you can distribute that build over Test Flight.