I have done a project where my ExtendScript was initiated from a FrameScript. In the other direction, there are several API Clients I use that can be called from ExtendScript, using the CallClient method. As for parameters, if all else fails you can set environment variables in one application and read them from the other side. AFAIK, environment variables are not permanent: when FM exits, the environment variables disappear. But as long as your session runs, they remain available. If no other parameter interchange with the API Cient is available, that method should always work.
Good luck
Jang