He is applying to colleges for a dual MD/JD program.
Ummm, I don't even think that is physically possible, just kidding - here's a link to the Baylor and University of Houston's dual degree programs, which this is one of the available options among M.D./M.S., M.D./Ph.D., and M.D./M.B.A: http://www.bcm.edu/education/dual_programs.cfm
It is, however, a pretty ridiculous and very ambitious plan. Let me first ask - what does he plan to do with both degrees - medical/pharmaceutical law or medical malpractice?
First, I will address your first question. No, you should be fine with the diversity you have in your academic career. Law Schools might even view this as a plus, but will most likely just not count it against you.
Secondly, your friend is going to have to apply only to schools that have programs such as this. He would be among a very select few specializing in both according to this site:http://md-jd.info/jd-md.htm
Which, he may want to check out and contact some of those people to see what they did. At the bottom of the page here
- those are some of the select programs that actually do dual MD/JD degrees. And I would assume that if he majored in something as difficult or at least thought of as difficult as biochemistry, these select programs would not hold it against him that he didn't have enough humanities if he does well on the LSAT.
If anything, he could take a few legal studies courses over the summer, but I would have to say that they wouldn't even really be worth it. Humanities in undergrad are a well known joke - especially to law schools and "superspecially" (haha) to Dual MD/JD programs.