Just to place it in a historical perspective, the Civil War ended in 1865, the Fisk Jubilee singers were founded or rose to prominence in 1871, and W.E.B. Du Bois enrolled at Fisk University in 1885 on a scholarship after having graduated as valedictorian in his high school class.
Many of the Jubilee singers were former slaves. Today, the choir has mostly commercial appeal and stands as a symbol of black history in particular and American history in general. During the years of its existence, however, it raised several interesting issues. The first has to do with the content of songs. The Jubilee Singers sing spirituals, or Black Spirituals in particular. This type of singing has its origins in the western Judeo-Christian tradition, and within the US is based on the King James Bible. Since slaves appropriated white songs, their singing was often considered subversive of slavery, and for many years scholars looked for encoded messages in the spirituals such as references to the underground railroad, passages to freedom, and other ways to circumvent white dominance. Published research today seems to be refuting this notion of subversive content, but does so primarily because of a lack of primary sources.Personally, I think the argument can be made either way, and the tradition of speaking in code is certainly reflected in African-American literature ( Frances Harper Lee's Iola Leroy written in 1892 has characters speaking about the Civil war in terms of what is going on at the market e.g.).
The second issue has to do with its choice of songs and its appropriateness. Mark Twain was a big fan of the choir early on and liked the way it reflected the old ways, but later on the Fisk Jubilee Singers were charged with selling out but such famous figures as Zora Neale Hurston for instance. The issue at stake is simply whether they should forever sing traditional songs the old way as sort of reminder about African American history, tradition, and identity, or if they can go with the Zeitgeist ( the spirit of the times) and modernize their repertoire with contemporary beats and rhythms. You decide.
Finally then, and that is proabably their single most important role, they can be considered guardians of history and tradition within the realm of a number of historically Black Unversities.