Just like "enhanced interrogation techniques," it turns out not to be a neologism. Here's an NPR commentary on the subject. Money quote:
We don't usually describe law-breakers as being illegal in themselves. Jack Abramoff may have done illegal lobbying, but nobody has called him an illegal lobbyist. And whatever laws Bernie Ebbers and Martha Stewart may have broken, they weren't illegal CEO's.
It's only your immigration status that can qualify you as being an illegal person, or that can earn you the honor of being "an illegal" all by itself. That use of illegal as a noun actually goes back a long ways. The British coined it in the 1930's to describe Jews who entered Palestine without official permission, and it has been used ever since as a way of reducing individuals to their infractions.