It is ilegal to hire an illegal alien but it is not illegal to be hired by an illegal alien. As long as you properly prepare the return, you should be OK.
Remember that people with ITIN do not get Earn Income Credit.
I just prepared 1999, 2000, and amended 2001 for a client. This client was using a fake social security number for those years but now he has his own social security number. His immigration attorney calls me and wants that all documentation to reflect his correct number. I said "that's wishful thinking. I cannot correct any W-2 that the client brings to me. My responsibility is to accurately prepare the 1040 returns for 1999, 2000, and 2001, and I have done that". I went on and said, even if you find the account that correctly prepared his 1999 W-2, based on the information at hand at that time, s/he cannot change that W-2 because the social security already has a copy of it and it is ilegal to do so".