I don't think it would really be a loophole. I'm certain that upon talking with the air-station the USCG helicopters were at would have brought up any problem, if it existed. I would be more concerned about the aircrews willingness to adopt non-standard procedures.There may be an easy solution to all this, and as mentioned above, talking to the USCG should be the #1 step before all else. Amateurs trying to find loopholes in the rules or other work around without talking to all the players involved isn't the way to do it.
For my part, I don't see working HF split as being any different than working a foreign country that has different amatuer HF allocations than the U.S..