Not at all. Despite some people, some veterans themselves, offering disparaging remarks towards 'civilians' writing military histories, a considerable proportion, perhaps even the majority, of military historians are not themselves of a military background, a demographic that has increased over time. Many however may develop associations with the military, many posts specialising in such being tied to military institutions, such as military academies like Sandhurst, or publishing through their own presses (an example from my recent reading being O'Hara's Torch, published by the Naval Institute Press).

Frankly, I wouldn't be concerned if you don't have military experience when writing military history; no scholar should hold it against you.