Frosted ear tips are somewhat common, you might also see tails shortened too, bulls testicals may frostbite (are you guys flinching?), we lost a calf in April because she was born on a 25-30 degree day (we don't consider that cold in the winter - that is normal to above normal) and didn't attempt to move, 110 lbs of stupid - She frostbit her hind legs almost to the hock and lost them both, frost bit the edges of her ears, her nose (though it healed normal) and most of her tail - but she didn't make it long after that. We have had calves born that instantly their coats frosted and froze but because they were active they didn't lose anything.
It depends on how cold the temp was (wind chill), what protection they may have had, moisture amount (wet coats). We have lost more "tagged" ears than non-tagged ones, obviously the tag impairs circulation or brings the cold "in" to the ear. When it gets cold we put down a lot of extra hay for feed warmth and also body protection as our main field now doesn't have trees for protection.
Since Brahmas are "warm weather" critters I doubt they'd like our Montana weather but I doubt they'd freeze to death at 30 degrees. If they were dry and had food they probably would just hang out until the sun came up and warmed up their backs!!