Yes. Your Apple TV is supported by Watch NRL if it's a 4th Generation Apple TV or higher.
Earlier Apple TV devices don't have an App Store and therefore aren't supported.
To stream the footy via your Apple TV, you'll need to set up your subscription via the Watch NRL website first. You won't be able to sign up via Apple TV.
Once you've successfully signed up to Watch NRL via a web browser, it's time to download the Watch NRL app.
Now it's time to log in with your username/password and start streaming on your supported Apple TV.
Note: The Watch Offline functionality is not available on Apple TV.