After making manual changes to the FTM-generated GEDCOM file based on output in the LST file, and using the method for correcting the media pathnames suggested earlier, I've managed to import the file with no error messages. I do, however, have a some questions:
1. What does RM do with user-defined tags? For example, the FTM GEDCOM file has _MILT entries for military service information.
2. I tried to use the FACT tag (GEDCOM 5.5.1) but it looks like RM doesn't like that tag. Should RM have handled FACT tags?
3. RE the pathname issue - is this considered a bug that RM will fix in the future? Maybe in the OS X native app?