See, I'm not entirely sure that Loken was fully controlled by Yogg. Because if he was, why would he deliberately set up a confrontation that ended in his death and the impending reformatting of Azeroth by Algalon?

My theory is that Yoggy can influence powerful titan/titan servants (I'm still not sure if the Watchers of Ulduar are intended to be considered Titans the same way that Golganneth, Norgannon, etc etc are) but he can't make them totally act out of character so much as he can emphasize/exaggerate their natures. So Mimiron becomes more interested in his gadgets than in lives, Thorim seeks sport through combat and forgets his duty (subtly aided by the 'Sif' entity created by Yogg), Freya becomes an avatar of nature's impartial cruelty and Hodir is lost in delusions of the rampaging strength of winter. We go in and slap them around, but Loken was too far gone for that.

So he sets up the Iron Dwarf army for Yoggy but he also sets us up to kill him, thus reformatting Azeroth and *once and for all killing Yogg-Saron*. The Titans couldn't kill the old gods without destroying the world, remember: since they're going to destroy the world anyway, it's a safe bet that they'll take the time to kill the old gods this time instead of letting them continue to interfere with the development of their experiment.

After Loken dies, Yogg's in a race against time to get out of Ulduar before Algalon arrives to sterilize the planet. If he can get out and enslave the mortal races, he'll have a power base from which to fight Algalon off and fortify Azeroth to stand against the Titans when they come to personally whup his butt. So he needs the Iron Army, but he doesn't *trust* it, since it (and Loken) are creations of the Titans and might regain their loyalties if pressed. He intends to use them as fodder in his war of conquest, and then discard them before it's too late. Hence his sticking them in front of the Archivum: he needs it guarded, but at the same time it's a relatively minor concern for him.

Likewise, Yogg himself is the one who lets the Twilights into Ulduar, much as C'thun made use of them in Silithus. They're insane cultists who worship the old gods via their elemental lieutenants, perfect minions because there's zero chance they'll betray him and side with the titans.

This is all speculation on my part, mind you.