Nope. If the boat is flying the flag of a nation we have a treaty with, our military can stop it. With no flag visible there is even less justification.
I think Bear Cub, once it was observed that cargo was being tossed overboard, one of two things could be noted:
1. The vessel was in distress and required assistance.
2. The crew was in the act of polluting the environment or destroying evidence of a crime.
I think any of the above constitutes grounds to investigate further by the USCG.