Since it is illegal to be here to start with, what makes you think the care about the tax law.
A few day's ago some Texas contractor came by my house, he was clearing the gas line for Duke Utilities, three 80,000 dollar tractors, all driven by Mexicans., I'd say if you ask duke utilities they would say it was a contractor sub contracted to a sub contractor, etc, etc.
I doubt they do. That was my point, they're violating it, as, in most cases, are their employers. In your example, Duke's sub-contractor contension would likely be valid. Presuming the contractor considers the drivers "sub-contractors", there's a good possibility that arrangement wouldn't pass muster, and if it did the driver would be responsible for remitting FICA. In my view, there's a lot of tax $ unaccounted for.