My 95lb chocolate lab is used to sleeping in a tent with us. So when we started hanging, he was curious, but not curious enough to hop in. Now, he likes sleeping directly under me and b/c I hang low, he likes leaning on me. Not sure why, but I think it's to make sure I'm still there.
I don't even know if I could sleep with him in a hammock. He would take up all the space just stretching out!