I am by no means an expert!!!
However, I watched the video a couple of times and will give my honest opinion.
Spook's body language appears very loose and wiggly, almost puppy-wiggly. His tail was wagging the whole time... It was wagging sort of high (though I don't know how he normally carries his tail, so its hard to be sure) but other than that he wasn't showing many dominance related behavior - at one point he was practically under Marq lol.
The bite looked like play to me as well. He wasn't getting much of a reaction from Marq, and probably wanted more. No doubt Marq growled at him... looks almost as if an adult dog is correcting a younger dog. How old are both of them again? Marq's tail was also wagging, but his ears were kind of flat - IMHO he looked like he felt trapped.
I am led to believe that if he wanted to hurt Marq, and was truly aggressive he would have already done so. Also, its hard to tell from the video because it ends after the nip and the growl, with them being pulled apart.
I agree with this:
edited to add:
I'll try and find my books ASAP
I was going to look for it today, but my friend (the one w Mia) wanted me and Maddie to go out to a couple pet stores with her and Mia for socialization, and to see how her training is progressing