There are many good reasons not to ally with the Twilight's Hammer. For one thing, they want to bring about the end of the world as we know it!
Yet some groups have, in a way, allied themselves with the Twilight's Hammer. The cult has sent ambassadors to Blackrock Depths with the intention of building a shrine over the Firelord's molten sanctum. While the Dark Iron dwarves do not yet trust the Twilight's Hammer enough to grant them access to the sacred caves, they have contracted members of the cult to run their prison, an arrangement that proves beneficial to both parties. Stories of the tortures which High Interrogator Gerstahn employs make even a Dark Iron's skin crawl.
At Blackfathom Deeps, a Twilight's Hammer sect works with a tribe of naga, but I believe this is an isolated instance, as I can find no evidence of a connection between the two factions on the whole. One occasionally hears stories of Twilight's Hammer sects joining with members of other chaos-oriented races or factions, but these alliances are short-lived, as dogmas and egos clash.
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