The DNS servers specified in the router configuration are for the router's benefit. The DNS servers specified as part of the DHCP configuration are for workstations, but won't provide anything unless the workstation requests DHCP information from the router.
If the workstations have static IP addresses, they won't send a DHCP broadcast, so they won't receive DNS or other setup info. Your choice is either to specify the DNS servers on the workstations along with the other IP configuration, or use DHCP.