Not really. 
For example, you can add your API key and attempt to create a prompt for Sonic Sage using the Headless Plexamp UI in a browser but, in my testing, it will not return any results.
Las time I checked editing posters was also not supported in the Headless Plexamp UI.
That said, you can still use the OpenAI features using your mobile App to update posters or target your Sonic Sage playlists to your Headless Plexamp Player