Is there any SQLite Manager for MAC OS X which is able to show ER Diagram?
You could give SQLEditor a go, check it out here. It supports using JDBC drivers for SQLite according to this page.
Admittedly, it's not free, but it does come with a 30 day trial period to determine if it's suitable for your needs.
As another option it seems that MySQL Workbench may be an option to use, as a plugin has been released supporting SQLite export read more about it here. I know from firsthand experience MySQL Workbench is reasonable to work with and it's available on OSX.
I use SQLiteManager and sometimes, Navicat for SQLite. Marco Bambini is the author of SQLiteManager and is very helpful and responsive. The people at Navicat are brilliant but the product is a bit pricy.
Also, note that for most SQLite3 databases created outside of xCode (and for use in iApps, the DB has to be converted to the proper format. Marco's SQLiteConverter works for that. Navicat does not have such an app.
Hope this helps.
David