Well--and that's not a bad idea, Pyrophoricity--how would we defend from such a dwarf?
Considering that we have personalities, how do they react with each other, as far as trust is concerned? What makes one dwarf trust another? In what ways do they trust each other? And what removes that trust?
If Meng has been born in the Fortress, if everyone knows him and if he has a good reputation, then he'd own a maximum amount of trust from the maximum amount of dwarfs. But if that's the case, how did he become a double-agent? If those reasons for trust don't exist, then how useful a sleeper would he be?
Were his parents sleeper agents, too? What were their reputations? What made Meng a killer of his fellow dwarf? Is his motivation political? Religious? Monetary? Or something else?
As far as use goes, in what way would key dwarfs and vital information be protected? What safeguards could we put in place, against this sort of thing? Could we outline areas of increasing security? Assign not only bodyguards, but also middle personnel, something like secretaries to public officials? If we can assign secretaries, can they then make appointments?
Can they be bribed or otherwise corrupted?
What does a dwarf have to do to be put in such a position of trust?
If key dwarfs are at risk, would assassins have the ability to track their regular movements? If they can, then ambushes might be plotted at points along those regular routes, where the key dwarf would be most vulnerable. Bodyguards might be taken out, or simply diverted/distracted from their charges. Maybe the bodyguards themselves could be corrupted, somehow? Is anyone completely incorruptible? If so, why?
What would motivate a key dwarf to put themselves at risk? What sort of "risky" dwarfs would they associate with, if any? What events would blur the distinctions between dwarfs "of a certain social position", and everybody else?
Would an assassin have the wherewithal to kill, and then commit suicide, even if they aren't in immediate risk of capture? If not, then a successful assassination might lead to the Fortress being locked down. Suspects might be interviewed. Trust issues might again be invoked. Our dwarfs can't take photos, and fingerprints haven't been invented yet--let alone data banks, so what kind of memory do they have? And what kind of memory aids? A successful assassin might return again and again, maybe in disguise. How like one dwarf does another dwarf look? What if the assassin is a human or an elf? Could dwarfs be expected to tell them apart?
How professional are the Professionals? Would successful assassins keep using the same tried-and-true methods? Would they notice that they were becoming more distinctive over time, or would they choose to ignore the risks, in favor of being an individual? Would their employers kill the killers?