Many things that are "illegal" are not crimes and you can't be prosecuted or charged for them. Many "illegal" things are merely breaches of contract or civil wrongs, and even then, money damages obtained in a lawsuit are not always the primary remedy that is available.
Outsourcing an employee is not generally a crime, although it might or might not be a breach of an employment agreement. This wouldn't necessary be a breach of the employment agreement as a default matter, however.
Most U.S. employment agreements are oral and only specify the rates of compensation to be paid and the general nature of the job to be performed, because the vast majority of U.S. employees are employees at will who can have their employment terminated at any time with or without cause (although employees fired without cause are entitled to unemployment benefits, while employees fired with cause are not entitled to unemployment benefits, and unemployment benefit claims rates affect an employer's unemployment insurance rates).
Of course, if there was a non-disclosure agreement (which would almost always be in writing) and it was violated, breach of that agreement would often give rise to a lawsuit, and infrequently but sometimes, to a criminal prosecution (especially if the non-disclosure agreement were to protect state secrets rather than trade secrets).
Leaking trade secrets (or state secrets) to from someone subject to a non-disclosure agreement to someone not bound by a non-disclosure agreement or in violation of one's own non-disclosure agreement could be a civil or criminal offense, but an NDA violation might be a very challenging matter to prove beyond a reasonable doubt in a criminal case.
The linked story doesn't make clear what kind of employment contracts Bob the software developer at Verizon (a major long distance phone company) had, or how sensitive the work he was doing was at that job. There are no indications that his surrogate ghost workers in China were anything other than private individuals doing software development work that Bob otherwise would have done. It doesn't seem to be a case of national security or industrial espionage. It is possible that Bob even had his Chinese workers sign a non-disclosure agreement.