Personally, I'm taking Torchwick's speech to the White Fang with a grain of salt. At this point there's no way to prove if that's what he actually thinks, or if it was just him playing to the crowd, and given how anime tends to work, I'm not gonna leap to hasty conclusions. And while the White Fang may be an army for them, it's fairly evident that this is an alliance of convenience that will end as soon as one side thinks they've won against their common foe and has a big enough dagger to stab the other in the back with.

Anyway, yes, Dust has a lot of energy given the explosion generated by the presence of particles in the air in Episode 2, and given the lack of gas stations and the like, I would say it's used as fuel, as well as other things. I guess I'm just trying to reconcile the dust store robbery also in episode 1 with 'let's build an army to fight a war'