Paladin and rogue in the same group - what's allowed and what's not?

[Menteith]

TBH I'm not even sure that the succubus paladin is legal. I know that at least some of those Fight Club monsters were illegal. I'm honestly not sure how to look at knifing her. I doubt even the force that granted her power would be quite sure how to call that one. In the other 99.999999% of cases I personally think that the fiend ganking wins. Even with D&D's absolutist alignment system some things are gray.

Alignment
Always - The creature is born with the indicated alignment. The creature may have a hereditary predisposition to the alignment or come from a plane that predetermines it. It is possible for the individuals to change alignment, but such individuals are either unique or rare exceptions. (MM1 p305)

I vaguely recall that "always" means 99% of a population, but I may be miscalling it. Regardless, fiend ganking doesn't win, as it's possible for them to not be evil, and killing people just because they ping the Detect Evil radar or because members of their race are generally Evil is murder.

EDIT
Nor is being Evil, in most places, a crime. A person can be an Evil individual who's in control of themselves and maybe kicks their dog sometime. An Evil person might break the windows on a church and sell booze to children. An Evil person might be a miser who charges people more money that they need to. That doesn't make murder ok. If you know that an individual is guilty of something, then one takes the appropriate action. If through inaction, you believe that others will come to harm, you take appropriate action. That's it.