This situation came up in our last game. The leading player went to the outer island where the Legendary Pirate (LP) was located. I wanted to use the Royal Navy (RN) Intercept card to send the RN to that island to fight the leading player. However, there is language in the Royal Navy section of the rulebook that says "the Royal Navy never fights Legendary Pirates" (paraphrased from memory). Does that language mean I can't send the RN to an outer island where the LP resides, even if another player is there?
Since this game can suffer from the runaway leader problem, I thought my strategy of having the RN and LP ganging up on the leading player was a good one. But if the RN is prevented from going to that island just because the LP is there, that would take away a good strategy.
This is a sound strategy and permissible by the rules. You just can't use the Royal Navy to help you gang up on the Legendary Pirate. But you can most certainly have the LP and RN gang up on the runaway Player.