Hi, sorry no, OmniOutliner does not have a similar command to write out as a flat file.
We store our files using SVN and made changes a long ago to make sure that it does work. If you're having trouble with it then we might able to help you get that straightened out. You should be storing OO files as a regular folder in SVN. Feel free to send me and email at
omnioutliner@omnigroup.com if you want to take this off-forums.