It is illegal for illegals to join the military, but at least 80 ‘dreamers’, who are illegal aliens have joined. Even though, Congress sets the rules and regulations of the military.
Be interested in your source for that figure. In any event, despite the fact that Obama's 2012 Dreamer amnesty is unconstitutional by my reading, the recipients (580,000 so far) are now legal under the law including being provided SSNs and work permits. So the military would have no choice but to accept them. They would be restricted in terms of security clearances.
The fact that we are kicking out tens of thousands of combat tested military as the military is downsizing makes it insane that we would recruit illegal aliens to take limited slots away from American citizens and legal immigrants is an obscenity.