Sorry, that was a bit confusingly worded - if the Macs are running OmniFocus 1.6.1, there's no problem.
Once version 1.7 syncs with your server, 1.6.0 or any previous build of the application just won't be able to understand what all the perspective information is doing in the database. That's what "not fully compatible" means.
If you're worried, you can grab OmniFocus 1.6.1 from
this link.