This gets argued about periodically. If you expose brass to ammonia, but load and shoot the loaded ammo promptly, you may never notice the effect. If you also anneal necks periodically, that helps prevent season cracking in ammonia's presence. If you leave the brass loaded for long periods and don't anneal, then even the small amount of ammonia gas that Jcwit allows into the air can do damage just by being present in the same room with the brass. Before annealing was worked out, soldiers used to cause season cracking of ammunition in the corners of ammunition stockpile bunkers just by urinating in those corners. The ammonia from the urine breaking down was all it took. Not a lot.
I should have made not that putting a small amout of Brasso on top of the media and allowing it to dry our for a few "there is one of the key words" few days in an open room ie; a garage then using the tumbling media will not harm the brass. I seriously doubt the amount of amonia gas left after a few days in an open room would be enough to harm any brass.
But then I think most of us now use liquid auto polish ie; Nu-Finish. I believe the only thing Brasso has going for it is its name.