A). Yes, it realy should. Do you approve of it, by any chance?
B). I am not sure if Dark Crusade is canon on where Deamons come from. Sacraficing units to get a better one is a fun mechanic. Is is true in 40k?
Nope.
As for deamons not needing to be things from the show: Whats the fun in that? We have so much to work with!