It shouldn't be a problem interisland for Hawaii - if they are the second leg there is a note that the rules of the initiating carrier apply to baggage policies - so, if the first flight is Allegiant, their rules apply. Consider checking the vest then. If you booked the flights separately for some reason, well you can always check with Hawaiian too. Great you have those e-mails. Print out all that stuff and keep it with the vest and you.