No. It is not mandatory.
The hotel cannot prevent anyone from taking the FREE shuttle boat from the airport into Vaitape. Then, it is a simple taxi ride to Le Moana.
Far cheaper than the hotel's boat and likely the same amount of time to get to the hotel!

So, if guests choose to take the hotel's transfer boat for that expensive cost, that's fine, it is your holiday and your money.

Think logically here: is Le Moana going to refuse to check you in to their hotel because you didn't show up on the boat?