I am not sure. Hel still has to play by the same rules as everyone else while the Dark One is a complete outsider. Hel is not planning to take away any of the gods' power just increase her own, maybe even enough to become top dog but she would not become any more powerful than Odin, Dragon or Marduk are at the moment. And to even get that far she had to make allies and promises. With the Snarl as leverage the Dark One wouyld not simply get the upper hand in their game, he would get to rewrite the rules entirely.