Walter is working on adding domain extensions to the Data Modeller. This will allow different domains to augment the model - such as custom annotations for JPA or OptaPlanner. Each domain is pluggable via a "facet" extension system. Currently, as a temporary solution, each domain extension is added as an item in the toolbar, but this will change soon. In parallel to this Eder will be working on something similar to Intellij's Tool Windows for side bars. Once that is ready those domain extensions plugged in as facets and exposed via this tool window capability. Here is a video showing JPA and it's annotations being used with the Data Modeller.
(Click to turn on 720p HD and full screen)