I just know. Just kidding, if you have a case for him being Se dom, I'd be willing to listen.
He's not much of a realist, lacks persistence and, while he enjoys fighting strong opponents, it's not for power. Overall, he's not consciously oriented towards the tangible or material aspects of the world. He's driven by arising opportunities and that which intrigues him, is exceptional in seeing talent and potential in others and the world, and is driven by the possibilities of fighting those with potential. It's more of a mental drive: "The idea of fighting someone talented" that he is chasing than a physical one. He doesn't seem like someone who'd be appreciative of either. Compare him to doms like Gon and Leorio who are impulsive and live in the moment. Those two could obviously use some foresight from those who can see developing trends, know when to act and not act, as well as how far to go, and they'd be appreciative of it. Hisoka doesn't need someone like that.