We had planned on upgrading our Windows 5.5 Vcenter servers directly to the 6.5 appliance using the migration assistant.
However I was informed by VMware that this would break SRM and we wouldn't be able to successfully upgrade SRM to a compatible version if we upgraded Vcenter directly to 6.5. So the question is does 6.0 have the same ability to migrate a Windows Vcenter with an embedded database to the appliance?
I ask because I remember that migrating with a local database wasn't an option with the fling that was available to migrate.
You can try migrate to vCSA 6.0 Update 2m first, see the following blog post for additional details: vCenter Server Migration Tool: vSphere 6.0 Update 2m - VMware vSphere Blog