without a paper trail it's impossible to say.

For instance, when I search my Hubbies DNA matches for his surname (Coan), almost everyone of the matches descend from what I will call the "German/New England" Coans. All with almost identical trees. It would be easy to assume that he, as a Coan, connects to that line somewhere....BUT he actually descends from the "Scottish-Irish/Southern" Coans.

This baffled me, until I had his mothers DNA tested.
She ALSO has all of those matches ... so they have no relation to his "Coan" surname and instead the connection probably comes somewhere from his mothers New England roots.

There seems to be a large group of DeWitts that have done YDNA on the Family Tree DNA site.
Google "DeWitt YDNA" to find it.
You may find your known line on there, which could help in your search, particularly if they have a close match with a DeWitt from another part of the country ... it could give you clues of where to look.

Good luck and happy hunting :)