I think to 'chance it' under the current regulations would be a serious error of judgement. Reading others' experiences, not only would the chances of getting caught & declined entry be high, but it could also spoil your friends' future Florida plans. I think this is the time for him to come clean, declare the conviction, apply for a visa and hope for the best. If he is refused - and there is a chance of that happening due to his earlier infingements - there may at least be other avenues open to try later; the door may not be closed indefinitely. But to try to sneak in again (if you will forgive the expression) could be equivalent to shooting oneself in one's own foot.