Redirect is the only way to retain search engine rankings though. That way once people get to the site through any of the domains pointing there the same domain is displayed to everyone (including the search engines). The search engines will therefore be able to recognise that links to any of those domains all point to the same site and not to duplicate sites on different domains.
You select which domain gets listed in the search results by deciding which domain to redirect the others to.
The DNS resolution is needed whether you do the redirect or not.