Most likely not. If you are in the US illegally, you almost always cannot obtain employment legally.
They didn't have visas, or they wouldn't be in the US illegally. If they were working using stolen identification, or they used false ID, they are guilty of two felonies right there. If the employer knowingly hired them illegally, the employer is guilty of a felony too.
Having over 200 illegals working on a farm means the certainty is very close to 100% that the above is true and there are plenty of felonies to go around.