Does anyone know whether the road in to the Mudro lake access point is maintained at all during the winter?

I believe it is, at least it has been in the past. Lots of snowmobiles to dodge on your way out there though. There is a "winter access entry points" thread pinned to the top of the winter camping and activities forum, I think you can find a more up-to-date answer there (scroll to the bottom of the thread to find the most up-to-date list).

After checking the list, it looks like the answer is "maybe". Perhaps when I've driven my car there in the past it was because the access roads had been packed down by snowmobiles, rather than plowed.

I would say no,unless things have changed. Sometimes logging operations come close to the landing. Check with USFS in Ely.

It is not plowed! My son tried a couple of years ago and the plowing stopped at the last cabin drive way. He tried to hike in and it was ALLOT farther than he rembered from where he parked.

last winter (2018/2019) it was not plowed. we were hopefully expecting it to be plowed but the last ~1 1/4miles were unplowed. we still did the trip, but didn't make it to fourtown on day 1 like we had planned.