Paul:
I talked with the super at Sankaty Head a couple weeks ago and though it was quite cold, they were open to their regular members. Given their location, I would imagine they are seasonal, but that might depend on ones personal tolerance of 40 mph wind and 35 degree temps
BTW, spring arrived March 20th
If the opportunity presented itself, I would not pass on the chance to play this course. It IS truly unique with a great history, very good routing and definitely F & F conditions. If you have time, go to windows live local.com and call it up. This will give you a very good sense of what you could expect.