Trying to get an offer from an American employer from Oxbridge may be more difficult (definitely more so than from an Ivy). Getting in to an American grad school from Oxbridge definitely would not be (any more than it would from an Ivy). American grad schools take in foreign students from foreign schools all the time. Being an American would only help compared to Internationals at a foreign school.
England could be something to aim for.
BTW, I think the worst he would do state-side is UW-Madison (though I suppose tOSU would give bigger scholarships).