Chaplains are disciplinarians of the Astartes. They keep the rank and file in line and watch over command and discipline.
A "spiritual way" it may be but it's all the same purpose.
Do you expect the Grey Knights to be in need of discipline on the battlefield?
Apothecaries stabilise battlefield casualties and extract the gene-seed.
Yet as the they fight the most terrifying of enemies all geneseed of those wounded by daemons would be useless.
As a matter of fact how do you expect to treat wounds from a Daemonblade?
As noted above, I find the existence of both of those specialties pointless.
Case closed. Lets not litter the topic.
