If a compliance rule to require device encryption is created and assigned to Windows Phone 8 devices, the compliance status will not display correctly for those devices. Even if a WP8 devices is encrypted, it will report in the policy as non-compliant.
In order to ensure that WP8 devices are encrypted, you can create a restriction profile with the Require device encryption option enabled. Though the device will report incorrectly in the compliance policy, it will actually be encrypted.
This issue has been given identifier CMDM-186896. This issue has been resolved with AirWatch 8.0 FP9.