Thanks, that could be true. i haven't thought about possibility number 2 and 3Several possibilities, all of which are fairly common.
1) They want the real snare sound, but also want to blend in a certain amount of triggered sound.
2) They use the trigger sound only on certain songs, the mic on others.
3) The mic goes to the audience. The triggered sound only goes to the monitors. This prevents any weird feedback loops from happening on stage.