Yep! After finishing the Lizard's Curse stories, Northcrest Conspiracy, Orc's War (trials), you'll get an invitation from the witch which will trigger Nameless visit at your home (4th nightmare).
There you get ONE CHANCE to choose your ultimate desire, and I chose to serve. Continuing the Orc's War story will lead you to the Plains of Death where you can have sex with Nameless. (not repeatable btw)