Cay, has he done Y-DNA testing? If he's a Hyatt then he should match one of the men in the Hyatt DNA project:
http://www.worldfamilies.net/surnames/Hyatt/resultsMy Hyatt line is in the project as well and I'm an amateur genetic genealogist, so if you private message me I can help interpret his results. I'll also look through my database for Sarah and see if anything pops up.
-Sunny