The kids I have access to is infact neutered. I'd love to have him dump his cum in my ass and knot me. But nonetheless he can still get hard. He will let me jerk him off and he will fuck me with excitement. He hasn't knotted me yet. And he does not cum. Once he fucks me for about 30 seconds he is done, no orgasms. And his erection goes away quickly. Is that because of the neuter? Or is there a method to keep him and his knot hard?
I've had a similar experience with a neutered golden retriever. He was a very good boy, energetic, had a great temperament. His sex drive was decent but when it came down to the act, he didn't have much follow through. I'm beginning to think that maybe it wasn't a sex drive at all and it was just humping for the playful/dominance thing at that point. He would hump anyone who would bend over for him and let him know that it was ok. One day, when no one was around, I dropped my pants just to see what would come of his humping instinct. He found his mark and his pace was hard and fast but, like your situation, there was no knot and no ejaculate.
Kind of sad, honestly, to see a dog in that state. Poor thing is missing out on all the pleasures of life. At least he doesn't know what he's missing...