Thank you.  There might be a pattern since he has hired one undocumented worker in each of the last two years.  My area of the country has seen ICE activity so he might be subject to enforcement. I think he should talk to an attorney.  

The Department of Justice has stated in its Immigration-Related Unfair Employment Practices guidance that “[a] person who uses a contract, subcontract, or exchange to obtain the labor of an alien knowing that the alien is unauthorized… shall be considered to have hired the alien for employment in violation of the Act.” (8 U.S.C. §1324a(a)(4); see also 8 C.F.R. §274a.5).