Tactics could be something that can be made functional in the game. However, how I explain how this will go out would probably lag many people's computers, so it could be a good idea to make it sort of "Do you want squad leaders/goblins/etc to use tactics Y/N?"
Anyhoot, I imagine that you can allow your troops to be commanded independently by their squad/militia commander (Maybe even a general). For example, Urist McTactic is traveling with 6 speardwarves and he is novice tactician. There is a line of 20-30 goblins supplemented by a few trolls. What could happen is that he makes a tactical mistake and tells his unit to charge instead of letting them come to him or splitting his forces into two. His squad ends up killing the goblins, but at a cost. You can tell where Im going with this. While also including this, you could also have your squad commanders "coordinate" and depending on their skill levels, a dice will roll to see how good they do together. So for example, a spear company of 6 dwarves coordinates with a company of 3 marksdwarves. The novice MD commander and the competent SD commander manage to work together fairly nicely, and by doing so, the spear company is constantly covered by marksdwarves who travel with the speardwarves, shooting over the speardwarves as they march in a line towards battle, i.e, covering fire.
How will they train is what I imagine to be through the use of "sandtables": Simulations of a battle on a table with sand that can be changed up to reflect terrains and have little figures be there for the movement of troops for the learning officer. I imagine this to be an inside thing, compared to the other thing I had in mind: Live exercises. Live exercises could be coordinated training drills between squads. In addition to training weapon skills, armor skills, etc, the commanders gain tactic skills. However, inorder to balance this, you'd have to make it so that the Tactics skill goes up slow and steady.
It would be cool if the dwarves could form a shield wall and advance, with some lighter dwarves forming a screenforce ahead while marksdwarves watch over from the cliff's above. However, I am sure this would be really hard to code, but if you could do it and it works, that would be brilliant.