I believe that being in close proximity to a certain structure and the nature around it would make it so undead don't appear, also the ulbukan territory hasn't been acessed by the likes of you and me for a very very long time, It's pristine nature so I'd assume things like human spirits and skeletons wouldn't be out there, at least thats how id explain the first part.

Second part I'd explain just the same. Closed gates, and it's a maritime city so they might have chocobos.... who knows

as to the third I wonder this myself... seing as how "Wild" the ulbukan territories are there certainly aren't very powerful NM's roaming around.