Unlike the other quests, which determine whether you have mages, templars, elves, or werewolves as your allies for the final battle, the resolution of the Orzammar questline doesn't matter for gameplay purposes. You get dwarven warrior allies regardless of who you put on the throne. The difference comes up in the epilogue. You can put the noble and honest Harrowmount on the throne--but he's a hidebound traditionalist who will end up isolating the dwarves from the rest of the world, hastening the decline of their civilization. Or you can put treacherous Bhelan on the throne, who murdered his brother (and if you're the Dwarf Noble, tried to frame you, his sibling, for the deed) and conspired with organized crime--but he's progressive and forward-thinking and will introduce much-needed reform that could save the dwarven people. Now that's a moral dilemma.