Yes, I'd assume that Strachan was a family name, also. If this were my ancestor, the first person I'd check would be the mother's or grandmothers' maiden names. Have you done that already?
Your David arrived in North America quite some time after Robert Strachan married into my Dawson line. There doesn't seem to be any corelation between your location in Vermont and my Dawsons' arrival in Niagara Ont.
It might be worthwhile to follow your family back and see whether they had once lived in the Tarland &Migvie area - abt 32 miles due west of the city of Aberdeen Scotland. You mentioned you were having trouble with this branch. If you'd like me to see what I could come up with, give me what you have on David (or Strachan Dawson) and what sources you have already checked