[whpalmer4]

I don't think there is, even with the Family Pack, though it might allow you to give out different credentials to each member of the "family".

Longer-term, my guess is that if Omni does ever opt to provide some sort of syncing mechanism that operates on a per-row basis (like OmniFocus), perhaps it will also make sense for them to package a WebDAV server in OO4 along the lines of how they did for OmniFocus, though probably the first choice will be to do it as part of the Omni Sync Service. Might be a good time for some feedback on the desirability of some sort of ad hoc collaboration setup.