Country music is as American as football / apple pie / insert-any-other-cliche-phrase-here, so it makes sense that, from time to time, the genre's artists would don some patriotic clothing.
Jason Aldean once called Nashville "Hollywood with a touch of twang," and rocker Shawn Mullins deemed Los Angeles "kind of like Nashville with a tan," so it's only natural that the stars from each city would intermingle -- personally and professionally.