I can never remember, do monsters get max hp on their first racial HD? What about npc's with npc classes? And npc's with player classes?
Karui Kage(Pathfinder Adventure Path Charter Subscriber; Roleplaying Game, Campaign Setting, Companion Subscriber)
During my conversion work with Legacy of Fire I had to do this a lot, and came to a conclusion. I later asked James Jacobs about it and he affirmed my thoughts, though pointed out that it's not always that big of a deal. But, generally:
Creatures with no racial HD (just class levels): First level maxed
Creatures with racial HD (whether or not they have class levels): First level not maxed
If you look through APs you'll see that, for the most part, this is the case. Sometimes they might give a particularly powerful NPC with racial HD the first level maxed anyways, and sometimes they don't max anything even if they have no racial levels. I'd say it's like the above 90% of the time.
According to the bestiary, creatures with PC class levels get their first class level HD maxed, while those with just racial HD or NPC class levels do not.