Hi.
The feature is not available in v3.0 so you can't add related entity columns to the girds view.
The only way to go about it is to add a new attribute to the opportunity e.g. new_businessunitname , create a callout on the pre create and assign messages and fill that attribute depending on the opportunity owner, then add the new_businessunitname to the grids view.
Cheers,
Adi