David Gaider stated that Anders being merged with Justice may have one of the two effects on his Calling:
"One is that the spirit within Anders can affect the level of his corruption, so it may delay or remove the necessity for his Calling altogether. Either that or at some point the corruption within Anders is going to corrupt the spirit." He refused to tell which one the writers prefer due to the possibility of Anders appearing in future games.
As for the taint itself, it is said that "The Black City taints those spirits foolish enough to draw too close.[9]".
Although it corrupts physically, I believe the corruption stems from the soul, corrupting a being's very essence, which is why it can also affect spirits. I think this is why Red Lyrium, unlike normal Lyrium, can affect living beings "psychologically" just by being near it, where no "physical" contact is required.
We also know from the "Learn More About Dragons" War Table Operation that they (Dragons) are blight resistant (I always choose Leliana)
Excerpt of Frederic of Serault's Report:
Within the carcass of the Abyssal High Dragon, we found cysts of hardened flesh. Sister Brigette, a scholar from Nevarra, said she had seen, once or twice, similar nodules in other beasts. To protect itself, the body grew a barrier around a foreign object that could not be removed. Naturally, of course, we cut into the cyst. The flesh within was blighted. We immediately examined all other cysts found in the other dragon carcasses. Each time, we found the blight. The only conclusion we can draw is that dragons can stem the spread of the blight within their own bodies. They cannot do this indefinitely, as the existence of Corypheus's dragon suggests, but they are more resistant than other creatures.
Dragons were said to "Rule the skies in a time before the veil" by Yavana in The Silent Grove comics. We know they were beasts of The Fade and have a link to the Elvhen people, who thought their form to be that of the divine (referenced in the sinner Codex).
This makes me think that the reason for their resistance is linked to spirits and The Fade somehow. It might perhaps also indicate they have had previous encounters with the taint, which is why they now have an inherent resistance to it.
Because of magic (an unknown variable, for the most part) we can't assume resistance to the blight has anything to do with genetics or evolution. A good example of this is circumstances surrounding modern elven breeding.
Patrick Weekes has further clarified that elf-blooded individuals could not produce an elven child together, as they are completely human (or dwarven, qunari, etc.) and inherit no elven genetics, etc., whatsoever from their elven parent.[8]
The elven genome has been described as "adaptive" and elven reproduction in this regard has "much more to do with magic" than science or simple breeding.
This can be explained through the Trespasser reveal, in which we know that ancient Elvhen people pre-veil were spirits who took physical form much like Cole and who could manifest in either form before the veil's creation.
Given what we know of spirits then this makes sense. Here is a Cole quote when he is made more like a spirit.
"It is here (The Fade) but held, constrained by a construct, veiled. Feelings, memories, minds, mortality: All shape it, a glass to hold water, we flow in the deep (Fade). Without you (Mortals), we (spirits) have nothing, not even us."
If spirits post-veil take shape through "mortals" and the Elvhen people's origin traces back to spirits, then it makes sense that their offspring adopt the "shape" of any race they breed with.
Anyways, all of this exposition to reinforce my point.
As for Dwarves, I've never heard anything about them being inherently resistant to the taint due to their "hardy" constitution, as some have mentioned on this thread. I'd like sources to back up those claims.
The seekers I believe are resistant to red lyrium corruption because of the spirit of faith who touched them and perhaps because they were made tranquil for a short time. Leliana's resistance I believe can be explained in the same fashion. The "visions" she believed she received from the maker as well as her faith which has always been a defining characteristic of hers, seems to be key.
All of this would again point to the taint being a corruption of the "spirit" or "soul" rather than something attributed to "physical" disease.
If Weekes decides to lea in favor of this quote
"One is that the spirit within Anders can affect the level of his corruption, so it may delay or remove the necessity for his Calling altogether
then it would further reinforce my beliefs, though because it's an undecided avenue, I won't include it in my arguments.
Anyways, this is a good subject to discuss, so thanks for starting the thread.