OH! I've always wanted to visit Alaska! I keep wanting to plan a trip there and then find myself drawn to warmer climates instead. You'll have to send me pictures when you get back!
You are in luck! As long as the company has a license to transport passengers for hire, then that flight should be eligible for travel insurance coverage. It would work just like it does if you are on a regular commercial flight. You can get reimbursement for the trip delay if the plane is delayed more than five hours. Let's not forget the weather there too. I watch those Alaskan fishermen shows and it seems like things can change at the drop of a hat so flights might be cancelled due to weather. If so, the travel insurance would cover you for added hotel stays, meals and give you reimbursement to get you caught up with the group you're touring with. Plus you'll be happy to know that all of the other parts of the plan you're used to will be there for you. So if you're hiking and someone gets hurt or sick the trip insurance will be there to help you with medical bills, or even medical evacuation since it sounds like you'll be in remote areas.
I certainly hope you have a fun time up there! Be careful on those glaciers and make sure Frank packs some extra warm socks for you. I hope you get to see everything I want to see. If it's bears, I hope you see them from a distance!