So let's see if I'm going to break everything with this method I read about elsewhere on the forums. On my Mac, I use Transmit to create a mountable disk using Omni Sync Server as a WebDAV server. Basically I created a folder called "OmniOutliner" on the root of my Omni Sync Server account. Then I mount that WebDAV as a disk (Finder will do this as well, I just find Transmit easier) which points to
https://sync.omnigroup.com/username/OmniOutliner.
On my Mac, I toss OO3 and OPML files in there. On my iPad I connect to the same volume (using the "OmniOutliner" path I created so as not to confuse things) and import the files to OO iPad. Then Export to WebDAV and do basically the same thing on my Mac again.
What's great is that Omni has built in a Rename or Replace function. As long as you never change the name, you can work right off the WebDAV disk on your Mac, hit save (it will take a bit more time than usual to save) and then simply replace the outline with the same name in OO for iPad.
This seems like it will work swimmingly, but I've got to ask, am I about to break my OmniFocus Sync? Is this an abuse of OSS in some way I don't realize? If so, there are other free WebDAV options, but I love keeping my Omni gear together. Let us know. And phenomenal work on OO iPad!!! Worth the wait!