Hi galen8,
eurorack is a specific MODULAR format.
The Oberkorn is a standalone unit, it's not an eurorack module, 84hp or not.
You can integrate it with your modular or not.
There are more examples of other music gear that is 3U high, and it's still not eurorack.
Making the module private is IMHO, the best way to handle this sort of gear. You still get to use your Oberkorn entry on ModularGrid.
Best.