Tab indented text is in fact the only format we work with (for retaining hierarchy). You should be able paste while in row selection mode (not editing something, can toggle with cmd-return) and it'll do exactly what you want. Or you can open it directly as a text file. OO3 does this as well. If this isn't working for you can you send a sample text file to
omnioutliner@omnigroup.com, please? Thanks!