If they had the additional manpower...no. But since they don't, and they have similar training like the Navy, it makes since they help secure our naval forces. And no, the Navy doesn't have the resources to maintain perimeters without shooting people out of the water. The USCG has small craft just about everywhere which can help maintain those perimeters.
That is not what I have seen, but that was 20 years ago. Almost every Navy ship has a Zodiac and even a motorized lifeboat with M-16s and a grenade launcher aboard could do the job proposed here. A USCG 41 footer is overkill IMHO.