I'd ask the native americans what they think, and respect their answer.

Based solely on what I have heard from some, a respectful homage to a specific well-known leader is quite different than a caricature of an entire tribe/people into a cartoony mascot for a sports team. It also makes a difference if you are monetizing their images for your personal gain.

But again, I'm the wrong one to ask. If you really want to know whether Hiawatha is an acceptable name for this specific project, I'd contact the current tribal leaders and ask.