Shetland is an archipelago, but ok. Historically populations in the Scottish islands moved around a lot more than you would think. Sick of the tiny village you grew up in? Hop in a boat and go to Orkney, or Skye, or Lewis. Travel by land was difficult, by sea was comparatively easier. There was also a lot of incomer traffic, from Ireland, Scandinavia, even the Baltic. So yes, there might have been a tiny fraction of genetic connection, but unlikely to be significant.