Is it possible to integrate Rasa with Keras framework model (deep learning or machine learning chatbot)?

Hi there, I’m comparatively new in chatbot world. I understand that RASA is a retrieval model chatbot, hence I have a done a simple chatbot in RASA NLU. And I have also done a generative model chatbot using keras framework. I’m wondering if these two models can be combined in RASA ? If yes how ? Does it have to be done using the Custom Action and Custom Policy call ?