Yes.
Military Civilians can be prosecuted under the UCMJ (Uniformed Code of Military Justice) and US Federal and State Criminal Codes.
Possibly, but probably not. American contractors were employed by the Federal Government, which put them under the same protection as our military; they would be prosecuted in the US, and under US law (see the April 2015 conclusions of the Blackwater-Iraq trials). Regarding the other part of your question; 'contractor' is not a status; a person is either military or a civilian; but regardless, if they are employed on behalf, or by the government, they are subject to American law.
No there are military contractors and DOD civilians
DoD military, civilians, and contractors
Service members and their dependents, DOD/GSA civilians, DOD/GSA contractors.
http://www.rememberthefallen.org/ This list is composed of military personnel and DoD civilians, and does not include civilian contractors.
Civilians
Those with convictions for trafficing, distribution, possession, and/or use are barred from enlistment in the US Military.
Only if they're civilians working for that military force.
American civil war
executives do not lead the military... civilians do. and civilians lead the military to prevent military coups. currently POTUS is Barrack Obama and SECDEF is Leon Panetta
The only civilians hired for work in military bases are cooks and maintance employees.
The military contractors lobby the government for contracts. In exchange for campaign funds, a number of representatives and senators will include these contracts in the government's budget. If it were only a question on the merits, there would be no reason for military contractors like Blackwater to be hired since contractors are no more effective that the US Military and cost more per soldier.