Norton Safe Search uses the ask.com search engine, the DNS service(btw the DNS service is powered by DynDNS) doesn't display the Safe Search page so you get no Safe Search results displayed if you go to a page that doesn't exist. All you get is this:
If you would be using Norton Safe Web toolbar however, then you would have the Safe Search included with it. Can be disabled though.
@rdmaloyjr: When Norton DNS was in beta it DID display the Safe Search web page but they removed that later, people were complaining about it.
@YoKenny: That's irrelevant, your link is talking about installable programs from Symantec, not the DNS service(which isn't something you install, you just set the DNS servers). Like i said, the DNS service doesn't display any Safe Search results.