the Create Operation is meant to work with any kind of entity defined into the Domain Model (persistent, volatile and subclasses).
If the entity you use is a subclass of another entity the Create Operation also create the instance of the super entity.
So in your case, with the Form, the Object and the Operation all set to work on the Requester entity it should also create the related instance for the User entity.
From what you wrote you have to change the Data Flow of the Form into a Normal Navigation Flow, otherwise the user won't be able to see a submit button.
Other points seems to be OK but I suggest you to :
- run the find model problems procedure (maybe there are model errors)
- place a breakpoint on the action and try to inspect the execution
Let me know if inspecting the model helps you to find the problem.