Manfred von Carstien allied with the forces of order during the storm of chaos campaign to repel the forces of chaos.
Armies I play:
the manfed thing makes more sense if you have read nights dark masters, 2nd edition WFRP book.
Chaos warriors could easily ally with order and vice versa. IE the super intelligent tzeentch warlord that allies with dwarfs and questing knights to destroy skaven that is plaguing his lands or destroy an enemy warlord that threathens to upset the balance. In short men can always ally with other men when their goals happen to be same. In the same manner men can always fight men when their goals oppose (empire civil war etc)
Err, no. That's not how it works. No one trust Chaos warriors. You are not going to see a Empire General having a friendly chat with the local Chaos Warlord about a seize fire and temporary alliance to wipe out a marauding Greenskin horde or anything like that. It's just not going to happen. There is no the enemy of my enemy is my friend. Chaos Warriors are literally servants of hell, complete with hideous mutants and demons and everything. Working with them is much worse than simply dying, it's risking your very soul. The only way a Chaos follower is going to be allied with any of the Human realms, Dwarves, High/Wood Elves is if they don't know it's a Chaos Worshipper.
I could see Dark elves fighting alongside humans or lizardmen against other disorder forces if they felt it served their purpose. maybe even alongside high elfs if matters were really dire. I'd however be really vary of being the order part in that battle, druchii aint known for loyality.
The true chaos worshippers don't trade much with the empire, at least not allowing the empire to know their identity.
Eh thats not the way its described in the hordes of chaos book. in one story there a norse and an imperial trader talk about feeding chaos spawn. and of people being chosen for greatness or damnation. that sounds like WoC to me.
Then he is a trader who has been to many different places so one must assume he is more open to other cultures than your average citizen.
With these two factors he still finds the were (forsaken probably) and the beliefs surrounding them heresy, he just doesn't find himself in a place where he thinks it's wise to say so.
I don't like the "order" and "destruction" labels as I think they oversimplify everything to an unnecessary and undesirable degree. Although alliances between factions under each heading are unlikely, it's not like all the factions of "order" are exactly best buddies either. Still, that's what we've got so we have to work with it.
As mentioned, I can see the Vampire Counts (Lahmians and Blood Dragons especially, also von Carsteins) working with anyone who'll take them so long as they gain from the deal. Whether anyone would have them is debatable, but a lot of the time the "order" party may not even be aware who they're dealing with, and a lot of the rest of the time they'll be desperate enough to take whatever's on offer. Mannfred fought alongside Imperial forces at the close of the Storm of Chaos, and although he tried to threaten them afterwards, there was no fighting between them.
I can imagine small warbands of marauders or orcs working as mercenaries or allies for those factions who might employ them. I can also imagine the Lizardmen making use of anyone from whatever faction so long as it gets the job done. Dark Elves might work with humans or Dwarfs while disguised as High Elves, and with humans openly if the humans are sufficiently gullible/desperate. Northern lords in the Empire might ally with Norscan chieftains to overcome a greater threat and turn a blind eye to their unusual worships (or simply not think there's anything wrong with them - see Knight of the Blazing Sun). In Sigvald an Empire nobleman travels north to ask for Sigvald's assistance because he thinks that something that radical is the only way to save the Empire. In The Red Duke a nobleman solicits the help of a Chaos cult in bringing down his hated rival. The Skaven might see surface-dwellers as useful to their own plots/plans and gullible humans might fall for their act - as in Skavenslayer where the head of the secret police was working with the Skaven and genuinely saw them as sympathetic and helpful. I can't see the Beastmen having much to do with anything to do with "order", admittedly.
The difficulty comes in getting the forces of "order" to accept the help. The elder races are less likely to tolerate anything that looks Chaos-y, and the Dwarfs wouldn't have any truck with greenskins full stop. The elves are more likely to be able to identify Dark Elves and presumably wouldn't have much to do with them afterwards (although Invasion! featured a group of radical druchii leaders genuinely seeking peace with Ulthuan, and there may be those in Ulthuan/Loren who feel similarly). The Lizardmen won't care so long as it's the right tool for the job; usually this means that Chaos is out, but greenskins and undead might be in. The Bretonnians and Imperials are the most likely to hook up with forces of "destruction", although I'd imagine they'd have to be pretty desperate - or naieve - to do so.
I think Daemons might be a more common ally than you'd think to Order. First of all, they have motivation: the little four way game/war means all kinds of crazy stuff might happen to further their patron's cause; or harm one of their rivals!
Second, possession: while the models don't show it, the fluff has shown that daemons can possess people and more-or-less still have their daemonic abilities at the ready.
Lastly, while Warhammer tends to focus on the 'Grrr kill smash' type daemon, I like to think of the 'Faustian deal' 'bargain with the devil' type who is seductive or tricky. "Come on... just one little sacrifice, and we will win this war for you... no one will ever know..."