Cisco IOS DHCP is having almost all features which is available in windows DHCP, if you are having difficulty finding how to add secondary DNS in DHCP, then it was your last day for that as this is very easy.
Command is same;
dns-server 4.4.2.2
now to add secondary dns;
dns-server 4.4.2.2 8.8.8.8
that’s all 