. . . a military uniform could include an instrument, and that a squad member would use it in certain cases, and the usage could effect how nearby friendly and enemy civ members fight, changing their willingness and focus in a fight.
So, in a word, Bards. Personally, I would vote
No, largely because of the age-old Bard problem: If you're able-bodied, you would be better off actually
fighting than trying to play a rah-rah cheerleader, and if you
aren't able-bodied, you'd be better off getting the hell out of the way. I've got nothing against the warriors themselves
yelling inspiring/terrifying/etc. battle cries while in combat, and even
singing, but if you're in a combat situation and find that your two hands are clutching a
musical instrument then you're doing it wrong. This might change during the Magic Arc, however, where enchanted instruments might indeed make Bards a viable option.
As for
non-Bards, yeah, I can see certain instruments being used to sound signals like "Enemy Sighted", "Caravan Approaching," "Raise / Lower the Drawbridge", "Shieldwall," ""Charge," "Defensive Retreat", etc. . . . but these a) would have to wait for such military actions to implemented in the first place, and b) are already in the game, what with its existing auto-pause warnings and civilian alerts. So your Hammerdwarves carrying bugles or whatever would largely be for flavor and that's it. Granted, I'm all for flavor, but we must admit that it pretty much stops there--unless actual magic is concerned, the most "effective" combination of musical instruments & military uniforms that I can think of is a marching band on parade. Which, admittedly, would be pretty cool.
In addition to this, I'd argue that a future military uniform expansion could be good for the multitude of roles one might need to be ready for a fight in. For example, wheelbarrows for near-combat item salvage,
Stretchers, and Stretcher-bearers, for hustling wounded dwarves out of combat ASAP. Although I can certainly see dwarves preferring to use the more utilitarian wheelbarrows instead.
documents pertaining to law or treatise so a member of militia can act as a diplomatic surrogate, or as an assistant or squire to such diplomats.
Such objects would work better, I feel, tied to the position of diplomat/clerk than to the actual military uniform.
Offerings, foodstuffs, . . . good luck charms, emblems,
Eating utensils, small tools, images of deities and/or loved ones, hair care items, games/toys, etc., could and indeed should be carried (or at least desired) by
all dwarves, civilians included.
At that point, why not expand uniforms to include civilians?
On a related note, why are there no leather gauntlets/bracers? I can kit my civilians out in leather armor, helms, and high boots, but their forearms (one of their most exposed parts, when fighting animals) are just sticking out naked.