There's a couple of mechs with enhanced pitching abilities (don't ask me to name any, I just know I've seen one or two, as well as heard about it from the devs) but why they didn't pick the Mad Dog is beyond me.
Mauler, Novacat, Hollander and Puma, I believe. None are first-choice AA, as they still cannot aim high enough to target divebombers.
The Vulture does look very fitting for AA. Perfect cockpit location, nothing keeping the arms from swiveling up, and missile racks already aiming towards the sky. Could be nice...