The I-485 form, Part 3, asks the following "yes or no" questions:
Have you ever, in or outside the United States:
a. Knowingly committed any crime of moral turpitude or a drug-related offense for which you have not been arrested?
b. Been arrested, cited, charged, indicted, fined, or imprisoned for breaking or violating any law or ordinance, excluding traffic violations?
c. Been the beneficiary of a pardon, amnesty, rehabilitation decree, other act of clemency, or similar action?
d. Exercised diplomatic immunity to avoid prosecution for a criminal offense in the United States?
As your friend is going to answer those questions honestly, your concern is moot. The USCIS will be aware of your friend's past legal issues by virtue of his honest answers to those questions.