I don't know who your leader of the Dol Guldur orcs will be, but do you really think he'll trust a dwarf leader of HIS orcs from the Mountain Galleries? I don't. Anyway, Har's lieutenant, Naglur, is just waiting for the right moment to take Har's place. Cut off Har's head and it's over, but... those are just suggestions; it's your game after all. Yes, the orcs of the Mountain Galleries are allies of the orcs of Sauron and Dol Guldur. The orcs of the Mountain Galleries, you could even say they're orcs from Dol Guldur, sent there some time ago.
p.s. yes I agree with you to reproduce the battle between the dwarves and the orcs of Moria at the East gate. I too would do it as it was told. This battle will be between the dwarves and the orcs of Moria who control the East gate. Sauron's orcs (Dol Guldur) will wait wisely and not interfere. As I said, the winner will be weaker and easier to kill.
Your ideas sound fantastic. I wish you a great campaign.
Arthur.