It really all depends on the historical accuracy and the prevalence in which that they were used. Although the Union did employ balloons as a reconnaissance tool with good results under the "Balloon Corps", they only fielded six balloons throughout their existence and were effectively disbanded in May of 1863. Furthermore, although the Balloon Corps was assigned to the Army of the Potomac during the Maryland Campaign, they did not arrive on time to be utilized by the commanders in any of the battles or skirmishes that took place.

As for the "Observation Towers" you're referring to, I couldn't find any information on that type of tower being used in the Civil War, as what you're describing sounds like it was made to be a permanent fortification or building, not constructed to be used in a specific battle. They did however have "Signal Towers" which would like to see in the game.