Apparently the Opera installer puts a few HKCU Netscape keys/entries/values in the registry referencing java items. Perhaps Sun did it, not Opera. Anyway ...
Software Uninstaller Custom Uninstall for the Netscape line lists those keys/entries/values. It also lists over 3000 files in C:\Program Files\Opera. After deleting the keys/entries/values with Custom Uninstall, the main list automatically refreshes and Netscape is still on it.
Now Custom Uninstall for the new Netscape line shows a few HKLM Netscape keys/entries/values referencing Opera items. It also lists the 3000+ Opera files. After deleting the keys/entries/values with Custom Uninstall, the main list automatically refreshes and Netscape is finally not on it.
Deleting those keys/entries/values does not seem to have affected my use of Opera. But perhaps Custom Uninstall should not list all those Opera files ...