The DHS personnel were not unidentified - they were in uniform with badges/tags, as for vehicles, nothing says that their vehicles used to tail the perps who are about to be picked up have to be marked, that would defeat the purpose of catching the responsible agitators.

The goal here is to avoid a massacre where violence escalates, to deescalate you identify and surveil the instigators (via a number of methods and intel work) then you simply wait for them to be separated from their herd and detain them.

Chad Wolf, after all.