Ack. You see, I had to put 'dub con' in the warnings, because some would be squicked by that, dream sequence or not. So I knew it would be misleading... but that's the chance I had to take. I thought of changing it to 'mild dub con', but by then I'd sent it in to the mod. :(
Originally it was real, but then it quickly became clear it was a dream (to show that Snape had become a bit obsessed with the wolf/Lupin by then through being in close proximity to Lupin for so long).