Yes, Hyabusa was reservation only, so get in advance. I waited until I got to Aomori station to get a ticket to Tokyo. Ended up in first row, next to the door, no view, and nowhere to put my feet.

First time I visited Noboribetsu Onsen I left by bus bound for Toyako. The bus stopped for a while at the new mountain that was growing, i think there was a ropeway also but I skipped. The bus went over by Toyako and there was a fine view of the lake caldera. Well worth the stop on the way to Hakodate.

Here is a TR by a person who did much the same trip. It includes N.O. and one foto is Jigokudaqni from Takimotokan: Active volcanoes in Shikotsu-Toya National Park (japan-guide.com)