In addition to https://webarchive.jira.com/browse/HER-351, you should have an option to prefer using the non-DNS resolves and then falling back to the dns lookup.
Attached is a patch with the suggested changes to the FetchDNS class.
The new settings property is a boolean called preferNonDnsResolves for the FetchDNS fetcher.
This option would help when you are inside of an private network and want to crawl a server on your own network by its public name. In that case you would prefer to use the local hosts files to specify the private IP of the server.