I would not put a lot of stock into the Mormon IGI files. They are not all that reliable when it comes to soldiers such as Harmon (or others for that matter). All the evidence that we have for the Gettysburg Death Roster points to death in a Federal Hospital at Gettysburg.
There are a number of soldiers wounded at Gettysburg who died in Richmond, but they all had ties to the city.
You will need to check every single soldier with the variant spelling W.H. or William Harmon/Herman in the compiled service records to prove conclusively that the soldier bearing the name W.H. Herman in your ancestor. That can be a tedious process unless the NPS Historian had the regiment or death date.