I like your idea, but I think it needs a little bit of a tweak.
I also think that it doesn't make sense that you can have both morgul orcs and dol guldur orcs in the same battle field. I also think that it would be nice to be similar to the dwarves where you can choose Minas Morgul or Dol Guldur.
Here's how the factions will work:
Minas Morgul:
Khamul will cost extra.
You will recruit Minas morgul orcs from an orc barraks inside the base (Morgul swordsmen are not free).
You will recruit Mountain trolls and Drummer Trolls from the Troll cage.
You will recruit Catapults and Battering Rams from the Great siege works.
You can recruit cheap mordor orcs from orc camp in the settlement, they are the vanilla weak orcs.
Instead of the Minas Morgul fortress in the outpost, there will be an outpost like the morgul tower which effects the entire map, for every morgul tower the enemy is weakend 5% or 10%. You can't build a lot since there isn't many outposts plus it's expensive.
And the other Outpost will be Cirith Ungul outpost instead of the normal barraks.
You can also recruit the Cirith Ungul heroes from there.
That's it for Minas Morgul.
Dol Guldur:
Witchking will cost extra
You will recruit Dol Guldur orcs from the an orc barraks inside the base (Dol Guldur swordsmen will not be free).
You will recruit Dol Guldur trolls from a Troll cage a long with These trolls which are bigger and more powerful
http://www.davidbordwell.net/blog/wp-content/uploads/Violence-troll-controlled-by-hooks-in-eye-sockets-3-as-Bofur-mounts-him.jpgI am not sure about siege... maybe catapult trolls? I think they're with the goblins. or maybe a mountain giant.
You can recruit Gundabad orcs from orc tents in the settlement, they are weaker than Dol Guldur orcs.
The outpost will be similar to minas morgul tower but, instead of weakening defense of enemies, it increases the damage of orcs by 5%. And for the other outpost as The Defiler metioned, you can recruit warg riders, castellians and spiders.
That's it for Dol Guldur.
What do you think of that?