How do the Dustmen formulate their position towards sentient undead? I'd think they'd view them as an antonym to the True Death. After all, undead like vampires, wights and liches live for an eternity and often choose this state to cheat death.
The Factol's Manifesto, on the other hand states that there are quite a lot free-willed undead in the Faction...
Skall, who is believed to be the founder of the faction and its only factol so far, has a very good reason of putting that caveat about intelligent undead into the rulebook.
The Dustmen do not believe anyone on the planes has gained True Death, so a vampire is as alive as a breathing guy.
I suspect the Dustmen have issues with some kinds of vampires. You know those stories where the vampire was made undead in the prime of his youth, then spends the rest of his immortal life indulging in decadence and debauchery? The Dustmen would hate those guys (well, as much as a Dustman could hate anything.) They'd say these vampires are wasting their gift of undeath by pretending to be alive -- as if their existence was some kind of Vampire Masquerade. 
Vampires have lusts and hungers that liches, for example, don't. I once designed a Dustman feat that allowed undead (or the living) who ordinarily craved blood, fear, life energy, or whatever to go without, acheiving a more passionless state.
Some Dustmen do believe that undeath is a necessary precursor to True Death. Skall himself seems to believe this, and all of the highest-ranking Dustmen are undead.
There is reason to doubt this; there are some living Dustmen who seem closer to acheiving True Death than Skall is, for example. But Skall isn't going to admit that.
In the hierarchy between the living and True Death, vampires are still probably closer to True Death than the living are (this doesn't mean they'll acheive it any faster; it just means they've reached a "more dead" state). Their cold flesh (when they haven't recently fed) and lack of a pulse is cited as evidence of this. Liches are closer still.
Is it known how one is supposed to make the ascension from the state of undeath to the True Death? As I understand it, Skall is regarded as a leader who delays his own achievement of True Death in order to gain more time to lead others to this goal.
Could it be True Dead, if you can neither die, nor live due to a lack of emotions?
The Nameless One from Torment, on the other hand, cannot die. The Dustmen apparently don't like that fact very much.
(Please let us view this topic primarily from an in-game perspective. Which means it should not be considered common knowledge that the upper circles of the Faction are undead.)
Is it known how one is supposed to make the ascension from the state of undeath to the True Death? As I understand it, Skall is regarded as a leader who delays his own achievement of True Death in order to gain more time to lead others to this goal.
Could it be True Dead, if you can neither die, nor live due to a lack of emotions?
The Nameless One from Torment, on the other hand, cannot die. The Dustmen apparently don't like that fact very much.
(Please let us view this topic primarily from an in-game perspective. Which means it should not be considered common knowledge that the upper circles of the Faction are undead.)
I'd like to know too actually, I've had them down graded to a sect in my last campaign because I wasn't sure how they were going to achieve anything. :\
Yes and no. The method is simple to state, but hard to actually do -- you have to rid yourself of all the emotions and desires of living. That's all.
This may sound a little weird, but it just struck me. Perhaps the Dustmen see the freewilled undead as something akin to a bodhisattva. In Buddhism, especially in Mahayana Buddhism, a bodhisattva is a being that compassionately refrains from entering nirvana in order to save others. Perhaps the undead dustmen higher-ups believe they have paused on the way to the True Death to help others understand.
Kind of macabre, but in a PS sense, it could work.
Oh, a lot of factions have philosophies that could be understood as versions or facets of Buddhism, especially for someone who takes their faction's views on a particularly mystical level.
The Godsmen: we are all on a cycle of reincarnation, even the gods (devas), constantly improving.
The Doomguard: Component things are impermanent and will inevitably decay.
The Fraternity of Order: one must study and embrace the Dharma.
The Signers: The material world is an illusion formed by consciousness and desires.
The Dustmen: perfection is the absence of striving or desire.
The Ring-Givers: meritorious and demeritorious karma will inevitably be realized as personal consequence.
According to Skall in the Factol's Manifesto, Dustmen believe that ironically, non-free-willed undead are probably closer to True Death than free-willed undead, but less able to comprehend this; however, free-willed undead are shorn of many of the needs and passions of the living and are generally closer to True Death than us. However, nobody still walking around on this side of the Great Wheel, undead or not, has fully joined the True Dead.