I just want to say that this is awesome stuff...as I'm still learning the system, I can't contribute to the theorycraft part of the discussion.
But I know weapons and explosives...master vampires should not be able to shrug off hellfire missiles. I know that the idea behind MHI is that the monsters are tougher...but they shouldn't be so tough that they can shrug off vehicular weaponry. The other point behind the MHI universe is that for the first time in history; our conventional weapons are at a technological level now where we can genuinely fight monsters on equal footing. I could see something like Lord Machado regenerating from a blast like that in about a day or so, but fire and heat are not particularly more effective against him/it either.
If you recall the lead-up to the battle for DeSoya Caverns, the other masters were more than willing to disregard the warnings that both Susan and Jager were offering them regarding modern weapons. And while even Jager might be a bit out of date with his knowledge (being a WWII "veteran"), Susan was and is right up to date with her knowledge of modern weaponry. The two of them knew to stay the hell out of that fight and rightfully so; though a lot of good hunters got killed that day, those masters got their asses handed to them, as they should have.
Anyway, MHI and that National Guard unit were only packing squad-based weaponry in that fight. The heaviest things that they had were man-portable anti-tank weapons and light AP mortars. The heavier munitions on gunships are enough to turn normal people into red paste. A couple of Hellfires should be able to put paid to a pack of "old fangs" in proper fashion; even with all of their regeneration. Unless the vampire is also casting rituals to protect itself, that kind of explosive force should be more than enough to put a master down. Hell...if they were packing a Carl Gustav; then that should have generated enough explosive force to separate a master's head from its body, so to speak.
But then what do I know...I'm still trying to figure this particular system out....