Its the same type of thing with Coast Guard officers in charge of LEDETs that are using naval vessels as platforms. It is not a violation of Posse Comatatus when a Coastie is in charge of the LE ops (even though he is military, his main mission is law enforcement) when he is riding on a Navy Frigate or destroyer sailing hundreds of miles out to sea enforcing U.S. Laws and Treaties. Its the Coast Guard doing the boarding, NOT the Navy.
This very rerason is why you will find Coasties working hand in hand with almoast every department of the Federal Govt. When it comes to the long arm of the law at sea, the Coast Guards jurisdiction is unmatched.
If the Founding Fathers could see us now.