I believe I've read reports that indicate the dirt sections are pretty awful to near unrideable when wet.
And pretty awful to near unrideable when dry
I attempted Windigo Pass last month (July). I was coming from the north. The first four miles of gravel are ok, but when I turned the corner onto the true
Windigo Pass Road, I was confronted with pumice.
I attempted to ride it for a couple minutes, but I didn't get far, between front wheel digging in and rear wheel spinning out. I decided to turn around. I ran into some fellow tourists a couple days later in Diamond Lake and they said they actually did ride it a few years back and considered it a nightmare.
As for traffic, there wasn't anything for the most part on the section I did. (If there was,
I may have hitched a ride!)
My advice: skip Windigo Pass.