Yeah, don't do that :)
Seriously, you don't want the iDisk sync feature messing around with your OmniFocus database. If you want to have the iDisk sync feature running, you should configure OmniFocus to save the database in the Backup folder, which is not synchronized by iDisk. This offers multiple advantages: you don't have to worry about the iDisk sync corrupting your database, and you won't have the CPU/network load involved in syncing your database, which is actually a directory full of files, masquerading as a single file. (Do right-click or ctrl-click on the OmniFocus database file and select Show Package Contents if you want to see what's in there).
You can read more about the alternative location for your database in this thread