Those are not ordinary Soldiers. They are trained law enforcement personnel from Fort Rucker. The Military Police perform identical missions as the civilian law enforcement and probably have semi mutual aid agreements in emergencies. Also, there may be a high amount of military personnel and families that live in the area off the installation.
Regardless if that is the case, they are still active duty military members who have no legal right to be policing American cities. That is why we have local, county, and state law enforcement.
Uh, no.
Military Police are supposed to only be used in a situation when it is proven that Military personnel are involved.
Mutual aid in emergencies does not normally include armed patrol. In a mass causality situation there would be coordinated efforts, but none would or should include armed patrols by active duty personnel.