As far as I know, UDD doesn't check the Asset Control database to see if a device is unmanaged or not. Most likely the device ended up somehow already in a deployment task and can be found under the Pending Unmanaged Client Deployments (Network view - Configuration). As a backup-plan, you can also use Database Doctor to export the devices first to .scn files before moving them to Asset Control. That way you still have a scn file you can copy to LDSCAN to be picked up by the Inventory Server Service again.
Frank