Question

How does HVR deal with non-logged unrecoverable operations, such as direct-path inserts (insert /*+ APPEND */) above the HWM into "NOLOGGING" tables?

HVR does support the capture of direct-path/append-hint/parallel inserts to regular tables, but tables defined as NOLOGGING tables are not supported.

Answer

When a direct path operation is performed on a table that has NOLOGGING defined (and the database is not in a force logging mode), generally the changes are silently ignored.

These direct path changes in Oracle are not recoverable.

If direct path operations on tables with NOLOGGING occur on the source (and they can't be avoided), you could consider scheduling online refresh after they happen.