You say this is very common but how common is it at the University of Illinois? I don't know the answer but I do know that the policy manual states:
No individual shall initiate or participate in institutional decisions involving a direct benefit (initial employment, retention, promotion, salary, leave of absence, etc.) to a member of the individual’s immediate family. “Immediate family” includes an individual’s spouse, civil union partner, ancestors and descendants, all descendants of the individual’s grandparents, and the spouse or civil union partner, of any of the foregoing. Each chancellor/vice president shall develop, for the approval of the president, university procedures to insure against such conflict of interest.
www.bot.uillinois.edu
Article IX, Section 2 Employment of Relatives
This being Illinois there is almost certainly an exception for some.