Do you have a reference to the fact of Emlyn being a place name only used as a given name in Wales after 1800? References such as Withycombe or Hanks, Hardcastle, and Hodges don't mention a place, but only the theories that it could come from Latin Aemilianus, or perhaps from an Old Celtic name which was "Latinized" as Aemilianus.
I do notice that Welsh Personal Names by Heini Gruffudd does mention a place, Newcastle Emlyn, in Dyfed, Wales, but it also says "could be from Aemilianus".
As an American, these entries seemed to imply Emlyn was in use before 1800, but I certainly assume that as a European closer to continental references that you are probably right and it's just one of many "Welsh" names introduced in the 19th century. :)