Hello, Mr. Brooke:
War of 1812 Vets that fought in the Civil War are not rare at all. One comes across them fairly often. I have even posted on the VA board the tale of a slave that fought in both wars.
http://www.history-sites.com/cgi-bin/bbs62x/vacwmb/webbbs_config.pl?page=5;md=read;id=11114