I will speak from my many years of experience as a participant in the war on drugs both domestically and internationally. The "war" is just a term in this regard, it does not follow the ROE of a military op.
Even when I flew on U.S. Customs Black Hawks over international waters accompanied by Bahamian authorities so that we could interdict in the U.S., Bahamas or int'l waters, weapons were not loosed unless engaged. Now, the Bahamians had a little more leeway in the aggression they might use on a Bahamian on their native soil, but it was not carte blanche.
We did not shoot down aircraft suspected or known to be carrying a load of narcotics into the U.S. from abroad. We did not blow ships out of the water. There were times that vessels, (fast boats and such), were incapacitated by firing at the engines and rendering them incapable of escape or ramming our vessels.
In this particular capacity the USCG is operating a police action as opposed to a military op. As in such ops, if there is peril to life and limb then the appropriate force can be brought to bear. If there were reason to believe that the vessel presented a grave danger to the U.S. (such as it contained military grade weapons and arms) then the matter could cross from a police action to a military one as the USCG has authority in both arenas.