I haven't taken this tour. I rented a car and drove up to Emerald Lake (about 75 miles). This is GORGEOUS! I was amazed at how much the terrain varied. I highly recommend it. It is much better (in my opinion) than the Whitepass Railroad as you go about twice as far. There is an Avis Rental Car in town, but book in advance!
Just thought I would offer you another option. BTW: Be sure to be on deck as you sail into or out of the fjord that Skagway is on. Many people miss this. It is very scenic.
This tour is out of Haines via a ferry from Skagway. There are postings of good sightings on the cruisecritic board. I would verify what the sighting were on the week last year that you are planning on going this year. They should have been keeping records? If not I would narrow down the percentage of sightings. I have to disagree- I have been on both the train and driven the Klondike Highway many times. The scenery from the train is superior at the summit and rich in history.
While fishing on Chilkoot Lake, we watched a mother bear bring 3 cubs to the shore. Our guide told us to be very quiet, and worked us in closer for better viewing. We watched as mama bear taught her cubs to catch the spawning salmon. Bald eagles gathered in the trees overhead to pick up the scraps. It was quite an experience, and I love to go back and look at the pictures I took that afternoon.
I would recommend the trip, but not through Dolley Varden. We had a bad experience last summer. Book thru the cruise line or check the boards for another vendor. Remember, when booking thru a independent all you have is a phone number when you get to your destanation. Which we had but no one answered. Surf around but on this one stay with the cruiseline.