The following post shows how to specifically allow specific DNS servers on a Cisco ASA firewall. In this example, I am using Google DNS to be allowed through the firewall.
DNS Rules
object-group service DNS-PORTS service-object udp destination eq domain object-group network GOOGLE-DNS network-object host 8.8.8.8 network-object host 8.8.4.4 access-list ACL_in extended permit object-group DNS-PORTS NETWORK 255.255.255.0 object-group GOOGLE-DNS