The only motor racing I've ever seen in the US where the anthem was NOT honored was motorcycle speedway (one barrel, no brakes, four laps) and that is the crowd they attract.
Will be at stadium auto cross in a couple of weeks and expect the same there - something about staduims and toilet bowls...
Sprints, Midgets, Stocks, and real motorcycles get a better crowd.
addenda: open wheel road courses are a 50-50 proposition, most drivers are not Americans and the fans tend to go all nationalistic every three minutes or so.