At this time in the military, it was customary that the royal family served in some capacity if they were of age/able to. This would often mean having some sort of officer role, though wouldn't necessarily mean seeing combat. However, bastard children of the king (like Don John) may have served closer to the front lines in order to gain some sort of status/elevate themselves from just being "the bastard son of whoever".

In the traditional sense of the role, an Aide De Camp would be used as a sort of secretary/personal confidant to a higher ranking officer. Tasks for an Aide de Camp would include administrative duties like scheduling the officer's appointments, supervising the officer's personal staff and acting as the go between for him and his staff, and helping with ceremonial work as well. In the UWL version of Much Ado About Nothing, this role is taken on by Balthasar.

The other type of military personnel seen in Much Ado About Nothing are Benedick, Claudio, Borachio, and Conrade. Given that Shakespeare doesn't assign particular military ranks to these characters, many scholars take them to be officers of some sort or another who are decently ranked, but not notable enough to have any sort of detail given to their role. Given their proximity to higher ranking officers like the princes, they themselves are likely also higher ranking.

Last but certainly not least among the military personnel in Much Ado About Nothing are Constable Dogberry, his deputy Verges, and the Watch of Messina. In most versions of the story the Watch are seen as an equivalent to the police in the sense of jurisdiction that they have/power they hold. In UWL's version, there is the added context that both Dogberry and Verges are veterans/used to be soldiers (given the time period, likely Crimean War veterans) who are now policemen.