eSnail,
I presume you are talking about the built-in functionality which allows you to use JPA-entities as variables.
There is no default support to use hibernate, however, there are 2 things you can consider:
1) Use Hibernate as JPA-provider?
2) Implement a similar solution as we did for the JPA-entities, plugging in a custom variable type (JPAVariableType) which save and loads the variables to the activiti db. This uses a custom session that
controls the EntityManager that is used to load/flush the entities used within activity processes. A good place to start looking is JPAVariableType and EntityManagerSessionFactory in the activiti-engine codebase.
