I would also take the DOL contact as "information" for your client. It actually infers "rights" as mentioned, OT, min wage, SS deposits, WC, etc. Do keep in mind if the employer continues to exist and cleans up their mess, the "wages" will likely go up, as a gross up is probably the cleanest for the employer to use, which will increase earnings for your client.
In the end, the increased wages is probably all you will need to worry about, since if your client had issues with what they earned, needed coverage for an injury, etc,. your client would have forced the issue earlier.
Si if needed/desired, do a sample return with the now wages as net, figuring the taxable as grossed up. The employer "covering" the employee SS and Medicare (and any other state required items) increases taxable for your client.