Brahmin went hostile in the area near New Vegas Medical. Is that normal? Haven't had any aggression up to this point.

I've run into several hostile brahmin in that area, however, I don't think it is a bug. You might find the majority Brahmin and Bighorners in domesticated situations, but in the wild they tend to be hostile.

I'll take a hostile Brahmin over a freeze any day.

i know where your talking about and i think its normal..ive also seen tame mole rats fighting hostile brahmin in that same area..