[-McSnip-]
It could very well lead to some discreet observations. If the King wants to attack the spawn lands, or the banshees, or at least pursue them if they flee after a major battle, he'd need to know the lay of the land, and the danger this jungle poses. Sending a few colonists in there and keeping them supplied over the years is a very low-cost way of withnessing the effects of the cursed jungle mist clouds, and how dwarves can react/defends against/use it. If he truly has a militaristic mindset, and likes to plan his battles, then the details of a zombie-creating jungle between him and his major opponents is definitely something he'd want to learn about. Claiming it was a clerical error is then just a clever way of not alerting the civilians to their purpose.
it's also a good way to get data about spawn movement outside their main bases, their numbers, and their tactics when dealing with our settlements. If the settlement DOES manage to endure and prosper in these conditions, then suddenly he has a stronghold he can use to start an inv cleansing into southern territory, with a well established supply route.
A civilian settlement would be a terrible idea for a scouting outpost (in my unprofessional opinion). It's putting civilians, most of which have families back in the main... empire... place-thingy in danger and, at best, will lead to unnecessary work for the Royal Archivist to cover the Royal Family's ass when they inevitably all die. A dedicated scouting garrison would have been far-better and also much easier to keep concealed from enemy detection, and also easier to evacuate in case of emergency, and finally less costly if everything goes bad and they all die.
Also, if we want to split hairs, the jungle does not create "zombies" (I actually turned off ALL random regional interactions so as to make the mist more likely to show up :V I'm a cheater). I'm pretty sure you meant mutants, though, and it's fairly-irrelevant to the main point of contention here, so blurble :V
E: please let this not turn into a drama please let this not turn into a drama please let this not turn into a drama
E2: Work has been started on a story piece! Here is a sample:
[...] a hidden passageway, which ramped upwards. Should one choose to then traverse this narrow, rough-hewn tunnel -- clearly not designed to impress -- they would find that it opened out at the end into a large, rough-hewn stone chamber filled with strange iron vats, cupboards, iron workbenches, and metal cages smeared with [...]
E3: Just as a small bit of commentary/possible discussion piece, I think this next one will be the last thing I write to feature the Royal Archivist, at least for a while, as I feel that I've been centering things too much on her and she'd probably be better in small doses.