It would have to be joined to the same vCenter Server which is also licensed for Essentials.
Is that a requirement for compliance?
That's a question better asked of the VMware licensing team.
The 3rd. Host on the remote location can also run as a standalone Host.... or join the vCenter on the the main site.
You are not allowed to reuse the vCenter a second time. You license package contains one vCenter Essentials Instance and 3x 2 CPU Lics for vSphere ESXi Essentials.