We went through Poughkeepsie on the 17th, it was open all the way through. We were up at Alta Lakes on the 19th - It did not look reservable and it was crowded - but this was a Saturday.
As far as camping right off the trails, we ran across areas that obviously had been camped at, like old fire pits - but it did not seem common on the bigger trails like Imogene/Ophir. It did seem common on Bolam Pass which connects HWY's 550 and 145. We camped in our 5th Wheel at Cayton Campground on 145/Bolam Pass road (great campground) but I bet reservations are hard to come by now.
If I was tent camping I would choose Bolam on the close side to 550 and catch a shitload of Brook Trout while I was at it.
Hope that helps, and I wish we were still up there.