Demons have subclasses: Succubus, Incubus being the obvious two. But there's probably more along the lines of Death Cultist, Hell Warrior, or Hell Lich that could have feasibly existed in Yggdrasil. 

More over the guild in the game was not run by justice worshipers, nor were they all good. Doux, and Greybeard made the guild with the intent of it just being a PVE thing but Doux would later help turn its aesthetic into more of a roman empire sort of deal. The guild's style was 'Man was King' hence why Claudius says 'Man is great for god needs man to bow to make him strong' or something along those lines. They're not goody two shoes they're law bringing, Knight Templar, conquerors. There is a branch of them like Dolton who see 'justice is the solution' but they only do so because 'law bringing is needed for order to exist'. They're not all Lawful, or neutral good. Claudius is flat out chaotic neutral. Severnus is Neutral Evil. 

The argument could be made because guild founder, and world disaster, BorntobeBad was undead. But he was also specialized heavily in damage magic, and the like as he was basically a walking talking AOE Nuke by the time the game ended. The closest they let in were undead, black mages, and the like. They didn't exclude others because of their race but because they didn't fit the aesthetic of the guild. For example having an overlord like Momonga would be weird when the primary defender of the guild are a bunch of knights in full armor, and grunts in silver armor its jarring.

Rogues don't typically buff stack. They debuff, and deal quick damage, and disable traps. They stab, mark, and allow allies to do additional damage.