Will try and give a bit of direction on your question.
The names on Roy's listing are generally provided when found by people doing research. I myself have sent him a number of names. So, there is a possibility of more names being found.
Why more Norwegians and Danes than Swedes in the army? Could be any of a number of reasons - Not many Swedes enlisted, not many Swedes in the South in General, etc etc.
In general, Scandanvians were not a large part of the make up of American at that time (as compared to English, Irish, German peoples), so there is a smaller pool of soldiers to dry from. In New Orleans, which was a very ethnically diverse City, there was a company formed, called the Scandinavian Guards, that was a volunteer company.
Hope this helps. I am sure more knowledgeable people will add to this.