Yes, the problem was first identified by the British in India as you suggest. My humble opinion is to err on the side of caution. If cartridge brass can be weakened by ammonia fumes from horse pee and the fumes aren't even strong enough to kill the stable boy, I'm not purposely going to subject my cartridge brass to anything with ammonia in it, neither horse pee nor Brasso.
I'm sticking with Flitz or Nu-shine. ymmv