If he is in the U.S. he must register as a broker / dealer to operate Bitfunder, whether he allows U.S. residents to participate or not.
What I don't understand is why does he not register? The person who bites the bullet and offers the first US legal Bitcoin stock exchange stands to become billionaire rich over the next decade. People join startups and risk 5 years of their life for an opportunity such as this. Ukyo stands to gain so much if he navigated the system instead of playing games.
Anyway, once the crowdfunding law comes into effect someone will dominate this space, be that Bitfunder or someone else.