I'm not sure if you could call Ishamael a regular Dreadlord/ Chosen..ever. Even before the Bore was drilled, he was advocating the meaningless of Creation. The Absence of meaning to it all. Even before the Bore was there, he was Shai'tans champion, so to speak.

I even think it's his books -extremely influential in many areas- that gave Shai'tan it's power. It's why -all of a sudden- this so-called True Power could be felt. It's the people who believed what Elan Morin had written that was the basis for Shai'tans so-called True Power.
I mean.... what else changed in the AoL that all of a sudden this new Power-source could be detected? There had been millions of channelers all over the world for thousands of years.
What changed was the existence of those books and enough people believing what was written in them.

If 'Belief and Order give strenght' to Creation (per Fel's words), believing in the Absence of Meaning and believing in the Disassembly of Reason give strenght to Uncreation. And isn't that exactly what Shai'tan represents? The absence of everything. Nothingness. It's the essence of Shai'tan.
He. is. Noting.

Ishamael never was a regular Dreadlord. It's what earned him his infamous name. He 'betrayed all hope' by becomming the Soul of Shadow. No other Chosen can say the same.

About the second part of this quote; if you can't channel, you just can't channel! It's irrelevant what source is channelled -be it True Source or the so-called True Power- you have to be able to channel first and foremost!
A non-channeler also can't use the True Power.

As a non-perfect analogy, consider the following;
If you don't have a mouth, you can't drink, regardless of the beverage.

Cheerioooow,
Mik

P.S:
I've seen theories that blame the sensing of Shai'tan on the weak-spot behind which is could be felt. But I think those are wrong. I think the weak-spot is the built-in place where Shai'tan is bound to the Wheel; the Soul of the Dragon.
How else could the Dragon "always be there to face Shai'tan"?
The weaving of the Dragon Soul into the Pattern (his birth) weaves the weak-spot into the Pattern.