Are you applying to the UIC MSTP(chicago) program or the UIUC medical Scholars program(urbana)? The UIC application says:
"The College of Medicine letters of recommendation, depending on their content, may need to be supplemented by separate letters submitted to our program office. One way or the other, our program requires at least one letter of recommendation from faculty or superiors familiar with your research. These letters should be mailed directly to the MD/PhD Training Program office (address in item 2 above)."
If you are applying to the UIUC program, the letters are due on December 31st I believe, so you still have time to get some. If you don't just list the names of the people who have written you letters.