My daughter just graduated from IU’s music school so I may be able to help.
IU does have ensembles for non music majors, for example the All Campus Orchestra with the following description:
“An orchestral ensemble designed for the Indiana University student with previous orchestral experience and whose academic major lies outside of the School of Music.”
Also they have private lessons and a host of music classes for non-majors. I remember this from my daughter’s freshman year as she was going over classes. There was an area for non-major which was quite long - from private lessons to dance classes to a variety of music classes in many genres. It’s a big music school so there are many classes.
Finally, there are a lot of “club” and/or outside activities. These seem to be organized year-to-year or organic depending on students. My D was a voice major interested in theatre so many of her friends were in an improv group that they organized on their own and could rent space at the memorial center and give shows. They sometimes would get a stand-up comic or a few instrumentalist to do “interludes”. Plus many of the restaurants and clubs have musicians play. This tends towards contemporary and jazz. There is just a lot of music and performance everywhere.
I hope this helps. The information on ensembles is here: http://www.music.indiana.edu/departments/ensembles/index.shtml
For questions on classes for non-music majors you may just want to call the music school.