If you were Pluto, permanent custodian and virtual prisoner of the Grecian netherworld, it's not clear what inciting war between Olympus and Asgard would get you as far as freedom from your assigned station. We obviously know what it would get someone like Ares, the god of war, who's been known to stoke such fires in the past between those realms (while making sure Earth became collateral damage in the process)--so an alliance between Pluto and Ares seemed the likely next step for these two, in a scheme which appeared tailor-made to provoke conflict between two pantheons of gods which maintained no formal relations between each other and thus might be quick to jump to conclusions if provided evidence of an act of aggression.
For instance, say, the lord of Asgard, Odin, learning of Krista, an Asgardian girl kidnapped and held captive by both Pluto and the son of Zeus.
(With Ares making a convincing Hercules, if only in striking an arrogant pose.)
As for what Pluto gets from hatching such a scheme, it still remains to be seen. To continue connecting the dots, we know what Hercules gets (the real Hercules), when Thor learns of Krista's fate: a good trouncing by the god of thunder, after which Thor is convinced by Zeus that Hercules is innocent, and that it's Pluto who's deserving of his wrath.
You'd think Thor's first thought would be to get word to Odin that Hercules and Olympus are in the clear as far as any warmongering; instead, he and Hercules engage in a contest to determine who gets to face Pluto in battle, a course of action which Zeus feels obliged to step in and correct with a few words of what we mortals might call "common sense."
But neither Ares nor Pluto are content to watch their carefully laid plans wither on the vine--and both know that it would only take the death of Thor to trigger a war of the gods!