If the flights are booked on separate tickets, which in this case it sounds like they would be since the Delta ticket is already purchased, there's no way to really protect yourself here in the case of a misconnect. It would be up to Hawaiian to rebook you and you would be at their mercy. Ultimately they would have no responsibility to rebook you for free and this could result in buying an expensive walk-up fare and losing your previous ticket as a no-show. They might show sympathy, but then again they might not.

One suggestion that might work if you run the numbers, is that if Delta is willing to sell a ticket direct to Maui or through Honolulu connecting on Hawaiian, and it's within your budget, you can cancel your existing Delta ticket for a credit (as long as it's not basic economy) and use it to rebook the new ticket. This way everything is on one ticket and you are thus protected from any misconnect liability.

As for luggage, you can request Delta to check your bags all the way to Maui even on separate tickets as they have an interline agreement with Hawaiian. You will need to show your printed Hawaiian itinerary to the Delta agent at bag drop showing the flight numbers. However, note that some agents don't know how to do this. Be prepared for having to ask for a "red coat" (supervisor) and even then they might not know how to do it.

If you do travel on separate tickets, I would make sure there is ample time between landing in Honolulu and departing for Maui. This way you have extra time in the event of a Delta delay, and also if you had to end up rechecking bags.

Good luck!