No the train does not stop but it is slow moving, get out and stand at the vestibule for your photos. No the summit bus is not a good option in my opinion, better is the bus to Emerald Lake, Yukon with the one way train.
Also be CERTAIN you have the Tundra Wilderness tour in Denali Park on your cruisetour. You will be VERY sorry if you only have the Natural History tour, a complete waste of time, as this is a TOP scenic area.
Take a look at a sample of possible photos for you if you go to the right areas. http://community.webshots.com/user/budgetqueen