Sorry, Not yet.
Although it is an interesting idea, i'm not sure exactly how it would work, because duckduckgo does not have a bot that could be used for local indexing at this point.
A privacy-conscious local search engine would be extremely handy though, and a nice alternative to google desktop.
There are some interesting local search engines available, so i'll get back when I remember some names
EDIT: I believe I misunderstood the OP; I thought they were referring to a local file search