Welcome to the Community,
this will most likely violate VMware EULA, which doesn't allow do combine he Essentials Kits with other editions.
Please see http://www.vmware.com/files/pdf/vsphere_pricing.pdf (page 5)
Essentials Kits are all-in-one solutions for small environments (up to three hosts with two CPUs each) .... VMware vSphere Essentials and Essentials Plus kits are self-contained solutions and may not be decoupled, or combined with other VMware vSphere editions.
In addition to the above mentioned license issue, you would most likely not be able to leverage vMotion, because the vCenter Server also needs to have a vMotion enabled license, which is not the case for the Essentials Kit..
André
Message was edited by: a.p.