I was hiked out of the Fish Creek Trailhead last Friday (10/18/19). My daughter and I hiked up to Fish Creek Saddle, and then to Grinnell Mountain on a use trail. The trail was fine up to the saddle, but obviously I can’t tell you how it was past that point. There were no other hikers up there, but I did see two pairs of hunters.
The road up is a fairly rough dirt road with high clearance recommended for vehicles. I took my CRV all-wheel drive and did fine, though it was very slow going.
I don’t know what the camping regulations are. If permits are available, it may be fine. You could always check with a ranger.