[jgb@etree]

Not sure if it's the same in BES 10, but I believe the policy option you're looking for in 10.1 would be:

Unified View for Work and Personal Accounts and Messages

Allow (default)

Specify whether the BlackBerry Hub displays work and personal accounts and messages together in a single view. If you set this rule to Disallow, the device must display work accounts and messages in a separate view from personal accounts and messages in the BlackBerry Hub.

This rule applies only to BlackBerry devices with a version later than 10.1.0

It's under the Software tab, listed in the group Rules for all devices.

HTH