Four DNS servers are added in the "Create Networks" panel of BOSH Director tile in Ops Manager web UI. However, we can find the first three entries in the configuration file resolv.conf in the VMs.
Up to MAXNS (currently 3, see <resolv.h>) name servers may be listed, one per keyword as per the Linux manual.
It is recommended to review the configuration of DNS servers and keep three in Ops Manager web UI followed by "Apply Changes".