If you want to order vmware ESXI separately to yourUCS serer then you can use one of the following the following SKU:
VMW-VSP-STD-1A=
VMW-VSP-STD-3A=
VMW-VSP-STD-5A=
Note that this does not include VCenter, just the license for the hypervisor, if you want Vcenter this is a separate SKU