Does regenerating an ORMIT™-OpenJava Oracle Forms migration erase edits? If we edit a migrated form, will a later regeneration overwrite our changes?

Not if you protect the file: any file of a migrated form can be protected against regeneration, and everything is versioned in Git. Most changes don't need a regeneration anyway:

• A change to a form's behaviour is made directly in its readable generated code, which has one trigger file per block.
• Changes to the screens are always safe, because the validation service runs only the form's logic.