I can see greys being accepted into any faith, to what degree of favor they recieve can be questionable; however, it depends on how they service the faith and how that specific faith accepts greys.
Sargas as an example:
Code:
Conflict is the Glory of the Soul. The Weak are beneath Contempt.
Mercy is for the Weak in both its giving and receipt; Honor and the
gift of Death is for the truly worthy foe. Conquest is resolution
and second to the conflict that glorifies His name. It is by such
lessons that The Smiter expects his Chosen to extend his Dominion
throughout these realms.
Such tenants inspire His priests, and draw His followers to the dark
banner.
Code:
help anarchist
Anarchist characters tend to be the most adventurous and fun-loving people
around. They have a devil-may-care attitude, and will go to any lengths to
make life happier and more pleasurable for themselves, often forgetting
about the consequences. They tend to be blind to the world around them,
concentrating more on self-gratification and self-indulgence, and thus,
ending up following only the laws that make sense to them. Although
friendly, they frequently prioritize their own pleasure above another's
well being.
I honestly could see a person who is an anarch to throw themselves into the faith of Sargas on a whim, and if it served them well, to continue as time progressed. The moment that the situation became hardpressing I would see them bailing unless they became honestly pulled into the faith and felt it in
their best interest to stay with the faith. Would this be appropriate for a member of the clergy to do this? I don't know... I would have to say it would be a case by case thing, and to make a blanket statement would be inappropriate.
-----------------------------------------
As for disallowing greys and lighties from the MC, that is an foolish statement. The MC isn't about Evil, it's not about conquest or oppression. The MC is about service to the Emperor. This can mean oppressive actions, or an expansive martial view on Pyrathia, but it is not "evil".
I could honestly see a scrupulous person in the MC, as a loyalist to his homeland. IRL's view on things see slavery as an evil, but if you are brought up with it every day it's impact becomes less an evil, especially if you feel it a necessary deterent to crime. It would be an interesting character who would no doubt be full of inner strife but it is possible.
Just my two copper.