Silver Searcher,
Curiosity is most welcome here, as that is the spark that drives further learning and knowledge.
The fact is that the American Civil War only encompassed 4 shorts years of our history, and then primarily in the South Eastern portion of the United States where Confederates forces are concerned. These serpent and snake buckles have seen a very long period of use, as you even pointed out, dating back centuries. Furthermore the evidence from excavated examples spans the globe, from Europe to North America, Australia, New Zealand, and without doubt countless points in between.
I have even read references to these types of buckles being worn by Canadian law enforcement officers into the early 20th Century. The point I hope to clarify is, that any particular recovered snake buckle, must be accounted for in context of area and other supporting finds, as well as construction style and design, rather than assigning a stereotypical assumption of usage.
On occasion, these snake buckles have been found, such as the example in Ironman's collection, in areas of America dating from a time period before there were Confederate States. Additionally from photo images and paintings of the 1850's through 1870's, we may note the popularity of these snake buckles in Australia and New Zealand, where they are seen to be worn by gentlemen that are not adorned in military fashion.
CC Hunter