Daisetsuzan National Park is open. Sounkyo Visitor Center have staff.
The Sounkyo Visitor Center is the core educational facility for Daisetsuzan National Park. Information about local wildlife is on display through video panels, a 3-D topographical diorama of the park, and taxidermy mounts of Hokkaido wildlife. There is a lounge space and a craft corner where you can create a memento of your trip. The eco-friendly facility uses natural light and solar power to reduce carbon emissions as part of conservation efforts at Hokkaido's largest national park.
The visitor center is also a useful place to plan routes for mountain hiking, with staff on hand to offer advice to hikers planning to tackle the more advanced trails on Mount Kurodake. Guide tablets with trail information in multiple languages are available to rent free of charge. Map panels display four recommended nature trails to observe the park's natural surroundings, with seasonal information such as the best photo spots for foliage in the autumn or blooming flowers in the spring. The Sounkyo Visitor Center is also situated near the starting point for the Kurodake Ropeway (cable car) that climbs up to the 5th station of Mount Kurodake.
Difficult to predict if "everything will be snowed in and inaccessible on foot (we are not interested in skiing)" in November. I wouldn't go in November if you worry. In Japan's Northern Wonderland, Winter Is Coming was published Oct 11 2017 and reported snow.
On October 1, a storm dusted Asahi-dake’s upper slopes with a half foot of snow and coated its summit with thick feathers of rime ice—the first snowfall in Japan this winter. By November, it will be buried under some of the driest powder in the world.
Appealing Things to do during Hokkaido Travel in November！
4. November Weather in Hokkaido
（Hokkaido’s highest / lowest temperature in November by Sapporo Kan Area Forecast HP）
As you can see from the figure above, the weather in Hokkaido during November in that transitional period between autumn and winter can vary from place to place.
Places like Hakodate in the southern area can be quite temperate compared to the northern, eastern, and Okhotsk areas that can get very cold, especially in the mornings and evenings.
The mountains in November are shedding their autumn colors. The snow doesn’t quite stick until December, so it is better to wait if skiing and winter sports are your thing.
The clear autumn weather continues throughout the beginning of November, but the skies slowly start to cloud as the first snows begin to fall. The snow starts to stick at the end of November signaling the start of the long winter.
The roads can be icy, so anyone not used to winter driving should take extreme caution. Please be careful!
https://japan77.net/top/life-culture/harmony-with-nature/how-to-enjoy-japanese-autumn/november/hokkaido-weather-november/#Weather_in_Hokkaido_in_November_overview has more on weather.