You need to talk to an immigration lawyer. Equity and employment are two separate issues. There should be no problem in giving him equity, since US law imposes

You need to talk to an immigration lawyer. Equity and employment are two separate issues. There should be no problem in giving him equity, since US law imposes almost no nationality based restrictions on ownership in a company. Getting him to legally work for the company is a different matter, and depends entirely on what visa he has.