This has nothing to do with dns resolution and doesn't matter until you decide to use your bot as a server in SSL connections (ctcp schat, telnet over ssl, hub in botnet linking). Read NEWS and doc/TLS for information on what's different in 1.8 and what new variables you'd need to set for some features to work.
Yeah, if your operating system isn't kind enough to report the nameservers to eggdrop, you have to set them manually, after the dns module is loaded. So dns-servers must be set in the config file after the loadmodule dns command.