It depends on the state. In California a citizen may use whatever force is reasonable to both stop a crime from happening and detain someone who has committed a crime in their presence until law enforcement arrives.
Granted, what is allowed and how it will actually play out are two different.
I personally don't have a problem with the military policing in a civilian environment. However, the military approaches law enforcement much differently than their civilian counterparts and I see that as being problematic.
In the situation described though, if the security forces guys were called, and the situation were serious enough, and they were closer or it would be in the interest of life preservation I don't see any reason why they can't send some of their guys to deflate the situation until civilian law enforcement arrives.
It's a simple courtesy. There are times even in the civilian world where one department will have jurisdiction and another department will occasionally respond to their calls because the handling department is busy, doesn't have the resources, are much farther away, etc.
SOURCE: I worked in LE for 3 years.