Before we went on our Hawaii cruise in 05 I tried to find a whale watching boat that would take me, my senior parents and my sister who is a quadreplegic. I couldn't find anyone that seemed to be accessible.
I did find out though that lahaina was a good port to go out of.
Well, when we got off the tender there were dozens of little booths where you could sign up for a tour that day! So we signed up for one, went had breakfast at an open air restaraunt right across the street on the corner (great macadamia pancakes covered with pineapple syrup!) and then got on the boat for a great tour, wheel chair and all.
Not that you need an accessible tour but no need to worry about finding something before you cruise cause there were dozens of operators right on the pier.
p.s. I've tried to attach a pic of us on the boat