Using the awesome power of "mode set", I have discovered and proven a few things about the game.
Fortress Mode and Arena Mode are very similar, as are Adventure Mode and Controlling-a-Creature-in-Arena Mode - to get to Fortress Mode from Adventure Mode, you must go to the second Arena Mode, remove control of the creature, and then set it to Fortress Mode.
The game defaults to the first entry specified for a type of object if none is defined - two examples are "toad" and "iron". "There are no idle toads or jobs" indeed.
Perhaps the ability to spawn a creature in Fortress Mode as a citizen could be added in another version/update?
Also, the game seems to define members of a civilized race as Hostile under a surprising set of conditions - using embark-tools to embark on a human fort had all soldiers hostile but the local law-giver Friendly. Using "mode set" proves that this seems to apply to any non-major historical figure - in a mass of hostile Human Bone Carvers, Farmers, and Engravers, a Bowman, a Lye Maker, and a Child were all Friendly for some reason, as well as the "adventurer", who was not my original due to "mode set" magics. Also, going from Arena Mode to Fortress Mode acts as if the game were under the effect of "reveal hell" minus the force-pause. Letting the game tick one frame lets the spoilers fly out, and going much further crashes the game.
More Research is required, preferably with more magma.