Doc: https://docs.openshift.com/container-platform/4.14/installing/installing_vsphere/upi/upi-vsphere-installation-reqs.html#installation-vsphere-installer-infra-requirements-networking_upi-vsphere-installation-reqs

In vpshere UPI installation requirements, we require all the nodes to be in the same VLAN. That's only correct in vsphere IPI because the keepalived VIPs can land on any node, so all nodes must be in the same subnet than the keepalived VIPs.

However, in vsphere UPI there are no such keepalived VIPs, so unless I am missing something, same VLAN (or, better said, same subnet) should not be a requirement (as long as other requirements, like latency or open firewall ports, are met).