Unfortunately we don't have any of these -- though we are interested. Part of the problem is the size of the system. For example, I've started to construct ER diagrams on a few occasions, only to find them too cumbersome to maintain. A partial ER diagram would be fairly easy to generate from e.g. MySQL Workbench, which can use a live database for source material; however, OJS is now well over 100 tables so such a diagram might be hard to use and maintain.
The best references are currently the Technical Reference and the SQL descriptors (dbscripts/xml/ojs_schema.xml and lib/pkp/xml/schema/*.xml); however, those aren't visual.
I wonder if the best approach wouldn't be to document subsections of OJS separately, particularly the content data model and workflow (as two separate pieces).
Note that there is a workflow diagram on the "About This Publishing System" page; it's user-oriented but provides an overall sense of data flow.
Public Knowledge Project Team