As a developer of many SOUNDBOARD applications I too would back this up. The amount of complaints and 1 star reviews we get because users feedback is something like - 'This app is crap, the sounds do not work, has a bug'
Sometimes if you are using a sound orientated app then I think there is fair argument to suggest overriding the silent mode is needed in certain cases. Why open a soundboard app and need to turn the sounds off? It is so sound orientated a user would not need to be in the app if they wished to have no sound, they would just exit it.
Anyone got any ideas? As I have seen apps in the app store that do this, and many many games too - so you can get it past review, maybe by luck though but could be worth a shot on an update, thus not rejecting the whole launch of an app for this function