Many illegals will be happy to put on the uniform for the pay and benefits. This has been going on for a while. I am certain that the man my late wife’s niece married is an Mexican illegal. Very dark skinned, classic cholo build and always looking down to avoid meeting my gaze,very limited English vocabulary. Made sure his wife quickly got pregnant and then again as as soon as possible. His parents showed up to live with him.Neither could speak word one of English. And this was in the USMC about 5 years ago.
The Romans depended on foreign soldiers, barbarians to man the Legions at the end. A society defended by men with no stake in it, no ties to it. It did not end well for them.